diff --git a/docs/packages/aws-lambda.mdx b/docs/packages/aws-lambda.mdx
index 2d8d40d1f..199be356c 100644
--- a/docs/packages/aws-lambda.mdx
+++ b/docs/packages/aws-lambda.mdx
@@ -70,7 +70,6 @@ const site = await deploySite({
 
 const handle = await renderToLambda({
   siteHandle: site,
-  planProtocol: "v2",
   bucketName: site.bucketName,
   stateMachineArn: "arn:aws:states:us-east-1:123456789012:stateMachine:hyperframes-render",
   config: {
@@ -88,10 +87,17 @@ const progress = await getRenderProgress({ executionArn: handle.executionArn });
 console.log(progress.status, progress.overallProgress, progress.costs.displayCost);
 ```
 
-Plan v2 is recommended for new integrations because workers fetch
-manifest-selected content-addressed artifacts. For backwards compatibility,
-omitting `planProtocol` still selects v1; existing callers do not change
-behavior until they opt in.
+Plan v2 is the default because workers fetch manifest-selected
+content-addressed artifacts. The SDK sends explicit v2 when `planProtocol` is
+omitted. Deprecated v1 compatibility remains available by passing
+`planProtocol: "v1"`.
+
+<Warning>
+  For an existing installation, pause new renders and drain active Step
+  Functions executions. Redeploy the Lambda handler and SAM/CDK state machine
+  from the same package version before upgrading the application SDK. Older
+  infrastructure may default omission to v1 or lack v2 support.
+</Warning>
 
 `renderToLambda()` validates the distributed render config before starting the Step Functions execution, so invalid dimensions, formats, chunk sizes, or payload sizes fail synchronously.
 
diff --git a/docs/packages/gcp-cloud-run.mdx b/docs/packages/gcp-cloud-run.mdx
index f7beacfe3..edf5317db 100644
--- a/docs/packages/gcp-cloud-run.mdx
+++ b/docs/packages/gcp-cloud-run.mdx
@@ -79,7 +79,6 @@ import { getRenderProgress, renderToCloudRun } from "@hyperframes/gcp-cloud-run/
 
 const handle = await renderToCloudRun({
   projectDir: "./my-composition",
-  planProtocol: "v2",
   config: { fps: 30, width: 1920, height: 1080, format: "mp4" },
   bucketName: "hyperframes-render-my-project",
   projectId: "my-project",
@@ -97,10 +96,17 @@ while (progress.status === "running") {
 console.log(progress.status, progress.outputFile, progress.costs.displayCost);
 ```
 
-Plan v2 is recommended for new integrations because workers fetch
-manifest-selected content-addressed artifacts. For backwards compatibility,
-omitting `planProtocol` still selects v1; existing callers do not change
-behavior until they opt in.
+Plan v2 is the default because workers fetch manifest-selected
+content-addressed artifacts. The SDK sends explicit v2 when `planProtocol` is
+omitted. Deprecated v1 compatibility remains available by passing
+`planProtocol: "v1"`.
+
+<Warning>
+  For an existing installation, pause new renders and drain active workflow
+  executions. Redeploy the Cloud Run image and Cloud Workflows definition from
+  the same package version before upgrading the application SDK. Older
+  workflows may default omission to v1 or lack v2 support.
+</Warning>
 
 Pass `projectDir` for one-shot uploads, or call `deploySite()` separately and reuse the returned site handle across many renders.
 
diff --git a/examples/aws-lambda/README.md b/examples/aws-lambda/README.md
index 3a04edb25..6c429820d 100644
--- a/examples/aws-lambda/README.md
+++ b/examples/aws-lambda/README.md
@@ -75,7 +75,6 @@ aws stepfunctions start-execution \
   "ProjectS3Uri": "s3://${RENDER_BUCKET}/projects/my-project.tar.gz",
   "PlanOutputS3Prefix": "s3://${RENDER_BUCKET}/renders/$(date +%s)/",
   "OutputS3Uri": "s3://${RENDER_BUCKET}/output.mp4",
-  "PlanProtocol": "v2",
   "Config": {
     "fps": 30,
     "width": 1920,
@@ -92,10 +91,20 @@ EOF
 
 The Step Functions execution kicks off Plan, fans out RenderChunk via
 the Map state, and finally Assemble. Final mp4 lands at `OutputS3Uri`.
-Plan v2 is recommended for new integrations. `PlanProtocol` may be `"v1"` or
-`"v2"`; absent still defaults to v1 for backwards compatibility. V2 uses
-separate manifest and content-addressed artifact locators throughout the
-workflow and never places a v2 object in `PlanS3Uri`.
+Plan v2 is the default when `PlanProtocol` is absent. V2 uses separate
+manifest and content-addressed artifact locators throughout the workflow and
+never places a v2 object in `PlanS3Uri`. The deprecated v1 transport remains
+available by sending `"PlanProtocol": "v1"` explicitly.
+
+### Upgrading an existing stack
+
+Pause new renders and let active Step Functions executions drain before the
+upgrade. Redeploy the Lambda handler and this state machine (or the matching
+CDK construct) from the same package version before upgrading the application
+that calls `renderToLambda`. The new SDK sends explicit v2 by default, while
+older infrastructure may default omission to v1 or lack v2 support. Keep
+passing `planProtocol: "v1"` until the infrastructure redeploy completes if
+you need a staged migration.
 
 ## Local invocation
 
@@ -112,10 +121,13 @@ sam validate
 sam local invoke RenderFunction --event sample-events/plan.json
 ```
 
-The `sample-events/` directory ships small JSON payloads for each of the
-three actions. They reference fake S3 URIs — useful for sanity-checking
-the handler's dispatch logic; not for full end-to-end testing (real S3
-calls require credentials and a project zip to actually exist).
+The `sample-events/` directory ships three tiers for each action:
+`*.json` demonstrates default v2 with `PlanProtocol` omitted, `*-v1.json`
+demonstrates deprecated explicit-v1 compatibility, and `*-v2.json`
+demonstrates callers that stamp v2 explicitly. They reference fake S3 URIs —
+useful for sanity-checking the handler's dispatch logic; not for full
+end-to-end testing (real S3 calls require credentials and a project zip to
+actually exist).
 
 ## End-to-end smoke + benchmark
 
@@ -124,7 +136,7 @@ the architecture works on a deployed Lambda — use the local smoke
 script:
 
 ```bash
-# Defaults use the fixture's meta.json minPsnr (30 dB for mp4-h264-sdr).
+# Defaults use Plan v2 and the fixture's meta.json minPsnr (30 dB for mp4-h264-sdr).
 ./scripts/smoke.sh
 
 # Customised:
diff --git a/examples/aws-lambda/sample-events/assemble-v1.json b/examples/aws-lambda/sample-events/assemble-v1.json
new file mode 100644
index 000000000..6dcc2aa8c
--- /dev/null
+++ b/examples/aws-lambda/sample-events/assemble-v1.json
@@ -0,0 +1,12 @@
+{
+  "Action": "assemble",
+  "PlanProtocol": "v1",
+  "PlanS3Uri": "s3://example-bucket/renders/sample/plan.tar.gz",
+  "ChunkS3Uris": [
+    "s3://example-bucket/renders/sample/chunks/0000.mp4",
+    "s3://example-bucket/renders/sample/chunks/0001.mp4"
+  ],
+  "AudioS3Uri": null,
+  "OutputS3Uri": "s3://example-bucket/renders/sample/output.mp4",
+  "Format": "mp4"
+}
diff --git a/examples/aws-lambda/sample-events/assemble.json b/examples/aws-lambda/sample-events/assemble.json
index 7e3ab4b9f..22d43c884 100644
--- a/examples/aws-lambda/sample-events/assemble.json
+++ b/examples/aws-lambda/sample-events/assemble.json
@@ -1,6 +1,8 @@
 {
   "Action": "assemble",
-  "PlanS3Uri": "s3://example-bucket/renders/sample/plan.tar.gz",
+  "PlanV2ManifestS3Uri": "s3://example-bucket/renders/sample/v2/manifest.json",
+  "PlanV2ArtifactS3Prefix": "s3://example-bucket/renders/sample/v2/artifacts/sha256",
+  "PlanHash": "0000000000000000000000000000000000000000000000000000000000000000",
   "ChunkS3Uris": [
     "s3://example-bucket/renders/sample/chunks/0000.mp4",
     "s3://example-bucket/renders/sample/chunks/0001.mp4",
diff --git a/examples/aws-lambda/sample-events/plan-v1.json b/examples/aws-lambda/sample-events/plan-v1.json
new file mode 100644
index 000000000..28e174110
--- /dev/null
+++ b/examples/aws-lambda/sample-events/plan-v1.json
@@ -0,0 +1,15 @@
+{
+  "Action": "plan",
+  "PlanProtocol": "v1",
+  "ProjectS3Uri": "s3://example-bucket/projects/sample.tar.gz",
+  "PlanOutputS3Prefix": "s3://example-bucket/renders/sample/",
+  "Config": {
+    "fps": 30,
+    "width": 1920,
+    "height": 1080,
+    "format": "mp4",
+    "chunkSize": 240,
+    "maxParallelChunks": 8,
+    "runtimeCap": "lambda"
+  }
+}
diff --git a/examples/aws-lambda/sample-events/plan.json b/examples/aws-lambda/sample-events/plan.json
index de6f7c12f..51bcf48ea 100644
--- a/examples/aws-lambda/sample-events/plan.json
+++ b/examples/aws-lambda/sample-events/plan.json
@@ -1,6 +1,6 @@
 {
   "Action": "plan",
-  "ProjectS3Uri": "s3://example-bucket/projects/sample-composition.tar.gz",
+  "ProjectS3Uri": "s3://example-bucket/projects/sample.tar.gz",
   "PlanOutputS3Prefix": "s3://example-bucket/renders/sample/",
   "Config": {
     "fps": 30,
diff --git a/examples/aws-lambda/sample-events/render-chunk-v1.json b/examples/aws-lambda/sample-events/render-chunk-v1.json
new file mode 100644
index 000000000..bc59ed151
--- /dev/null
+++ b/examples/aws-lambda/sample-events/render-chunk-v1.json
@@ -0,0 +1,9 @@
+{
+  "Action": "renderChunk",
+  "PlanProtocol": "v1",
+  "PlanS3Uri": "s3://example-bucket/renders/sample/plan.tar.gz",
+  "PlanHash": "0000000000000000000000000000000000000000000000000000000000000000",
+  "ChunkIndex": 0,
+  "ChunkOutputS3Prefix": "s3://example-bucket/renders/sample/",
+  "Format": "mp4"
+}
diff --git a/examples/aws-lambda/sample-events/render-chunk.json b/examples/aws-lambda/sample-events/render-chunk.json
index 46d191ae2..51959bd8e 100644
--- a/examples/aws-lambda/sample-events/render-chunk.json
+++ b/examples/aws-lambda/sample-events/render-chunk.json
@@ -1,6 +1,7 @@
 {
   "Action": "renderChunk",
-  "PlanS3Uri": "s3://example-bucket/renders/sample/plan.tar.gz",
+  "PlanV2ManifestS3Uri": "s3://example-bucket/renders/sample/v2/manifest.json",
+  "PlanV2ArtifactS3Prefix": "s3://example-bucket/renders/sample/v2/artifacts/sha256",
   "PlanHash": "0000000000000000000000000000000000000000000000000000000000000000",
   "ChunkIndex": 0,
   "ChunkOutputS3Prefix": "s3://example-bucket/renders/sample/",
diff --git a/examples/aws-lambda/scripts/smoke.sh b/examples/aws-lambda/scripts/smoke.sh
index d90d46f71..f2f2ff6c9 100755
--- a/examples/aws-lambda/scripts/smoke.sh
+++ b/examples/aws-lambda/scripts/smoke.sh
@@ -31,7 +31,7 @@
 #   --region <region>          (default: $AWS_REGION or us-east-1)
 #   --profile <name>           (default: $AWS_PROFILE, otherwise the AWS
 #                               default profile resolution chain)
-#   --plan-protocol <v1|v2|both> (default: v1)
+#   --plan-protocol <v1|v2|both> (default: v2)
 #   --keep-stack               (skip `sam delete` at the end)
 #   --skip-build               (skip the ZIP rebuild; use the existing one)
 #
@@ -82,7 +82,7 @@ SMOKE_RUN_ID="${HYPERFRAMES_SMOKE_RUN_ID:-$(hf_new_smoke_run_id)}"
 STACK_NAME="${STACK_NAME:-hyperframes-lambda-smoke-${SMOKE_RUN_ID}}"
 AWS_REGION="${AWS_REGION:-us-east-1}"
 AWS_PROFILE="${AWS_PROFILE:-}"
-PLAN_PROTOCOL="${PLAN_PROTOCOL:-v1}"
+PLAN_PROTOCOL="${PLAN_PROTOCOL:-v2}"
 KEEP_STACK="false"
 SKIP_BUILD="false"
 REQUIRE_ENCODED_SHA_EQUAL="${REQUIRE_ENCODED_SHA_EQUAL:-false}"
@@ -110,7 +110,7 @@ Flags:
   --stack-name <name>           SAM stack name (default: hyperframes-lambda-smoke-<unique-run-id>)
   --region <region>             AWS region (default: $AWS_REGION or us-east-1)
   --profile <name>              AWS profile (default: $AWS_PROFILE)
-  --plan-protocol <v1|v2|both>  plan transport(s) to compare (default: v1)
+  --plan-protocol <v1|v2|both>  plan transport(s) to compare (default: v2)
   --reserved-concurrency <N>    Lambda Map MaxConcurrency cap (default: 16)
   --keep-stack                  skip `sam delete` at the end (manual teardown later)
   --require-encoded-sha-equal   also gate byte-identical encoded MP4 output
diff --git a/examples/aws-lambda/template.yaml b/examples/aws-lambda/template.yaml
index 7ae0b7f6f..8e47da3eb 100644
--- a/examples/aws-lambda/template.yaml
+++ b/examples/aws-lambda/template.yaml
@@ -222,12 +222,12 @@ Resources:
               - Variable: $.PlanProtocol
                 IsPresent: true
                 Next: UnsupportedPlanProtocol
-            Default: Plan
+            Default: PlanV2
 
           UnsupportedPlanProtocol:
             Type: Fail
             Error: PLAN_PROTOCOL_UNSUPPORTED
-            Cause: PlanProtocol must be "v1", "v2", or absent (defaults to v1).
+            Cause: PlanProtocol must be "v1", "v2", or absent (defaults to v2).
 
           Plan:
             Type: Task
@@ -236,6 +236,7 @@ Resources:
               FunctionName: !GetAtt RenderFunction.Arn
               Payload:
                 Action: plan
+                PlanProtocol: v1
                 ProjectS3Uri.$: "$.ProjectS3Uri"
                 PlanOutputS3Prefix.$: "$.PlanOutputS3Prefix"
                 Config.$: "$.Config"
@@ -391,6 +392,7 @@ Resources:
                     FunctionName: !GetAtt RenderFunction.Arn
                     Payload:
                       Action: renderChunk
+                      PlanProtocol: v1
                       ChunkIndex.$: "$.ChunkIndex"
                       PlanS3Uri.$: "$.PlanS3Uri"
                       PlanHash.$: "$.PlanHash"
@@ -427,6 +429,7 @@ Resources:
               FunctionName: !GetAtt RenderFunction.Arn
               Payload:
                 Action: assemble
+                PlanProtocol: v1
                 PlanS3Uri.$: "$.Plan.PlanS3Uri"
                 ChunkS3Uris.$: "$.Chunks[*].ChunkS3Uri"
                 AudioS3Uri.$: "$.Plan.AudioS3Uri"
diff --git a/examples/gcp-cloud-run/README.md b/examples/gcp-cloud-run/README.md
index 62732f992..0f92ca826 100644
--- a/examples/gcp-cloud-run/README.md
+++ b/examples/gcp-cloud-run/README.md
@@ -8,7 +8,7 @@ Cloud Workflows adapter for HyperFrames distributed rendering.
 
 ```text
 scripts/smoke.sh        Owner-isolated real-GCP deploy, render, parity, cleanup
-sample-events/          v1 and v2 handler request examples
+sample-events/          Default-v2, explicit-v1, and explicit-v2 request examples
 ```
 
 The Terraform module and Cloud Workflows definition live in
@@ -16,8 +16,9 @@ The Terraform module and Cloud Workflows definition live in
 
 ## Protocol rollout
 
-The workflow defaults to plan protocol v1 when `PlanProtocol` is absent. V2 is
-accepted only when the caller explicitly sends `PlanProtocol: "v2"`.
+The workflow defaults to Plan v2 when `PlanProtocol` is absent. Deprecated v1
+compatibility remains available only when the caller explicitly sends
+`PlanProtocol: "v1"`.
 
 V1 and v2 use disjoint plan locators:
 
@@ -26,9 +27,15 @@ V1 and v2 use disjoint plan locators:
 
 The workflow validates that the plan response matches the selected protocol
 before starting chunk fan-out. It never silently falls back from v2 to v1.
-Deploy the v2 workflow only with a Cloud Run image whose handler implements
-the matching v2 request/response contract. An older v1-only handler will keep
-serving default v1 requests, but explicit v2 smoke executions will fail closed.
+Deploy the workflow only with a Cloud Run image whose handler implements the
+matching v2 request/response contract.
+
+For an existing installation, pause new renders and drain active workflow
+executions. Redeploy the Cloud Run image and workflow from the same package
+version before upgrading the application SDK. The new SDK sends explicit v2;
+older workflows may still default omission to v1 or lack v2 support. Keep
+passing `planProtocol: "v1"` until the infrastructure redeploy completes if
+you need a staged migration.
 
 ## Prerequisites
 
@@ -40,7 +47,7 @@ serving default v1 requests, but explicit v2 smoke executions will fail closed.
 
 ## Run the smoke
 
-V1 remains the safe default:
+Plan v2 is the normal smoke path:
 
 ```bash
 ./scripts/smoke.sh \
@@ -120,12 +127,17 @@ old invocation's state or image implicitly.
 The sample events mirror the request bodies sent by Cloud Workflows:
 
 ```bash
-# V1
+# Default v2 (PlanProtocol omitted)
 curl -sX POST localhost:8080/ \
   -H 'content-type: application/json' \
   --data @sample-events/plan.json | jq .
 
-# Explicit v2
+# Deprecated explicit v1 compatibility
+curl -sX POST localhost:8080/ \
+  -H 'content-type: application/json' \
+  --data @sample-events/plan-v1.json | jq .
+
+# Explicit v2 for callers that always stamp the protocol
 curl -sX POST localhost:8080/ \
   -H 'content-type: application/json' \
   --data @sample-events/plan-v2.json | jq .
diff --git a/examples/gcp-cloud-run/sample-events/assemble-v1.json b/examples/gcp-cloud-run/sample-events/assemble-v1.json
new file mode 100644
index 000000000..4be98aa21
--- /dev/null
+++ b/examples/gcp-cloud-run/sample-events/assemble-v1.json
@@ -0,0 +1,12 @@
+{
+  "Action": "assemble",
+  "PlanProtocol": "v1",
+  "PlanGcsUri": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/plan.tar.gz",
+  "ChunkGcsUris": [
+    "gs://hyperframes-render-PROJECT/renders/hf-render-demo/chunks/0000.mp4",
+    "gs://hyperframes-render-PROJECT/renders/hf-render-demo/chunks/0001.mp4"
+  ],
+  "AudioGcsUri": null,
+  "OutputGcsUri": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/output.mp4",
+  "Format": "mp4"
+}
diff --git a/examples/gcp-cloud-run/sample-events/assemble.json b/examples/gcp-cloud-run/sample-events/assemble.json
index 4be98aa21..1b4ebf282 100644
--- a/examples/gcp-cloud-run/sample-events/assemble.json
+++ b/examples/gcp-cloud-run/sample-events/assemble.json
@@ -1,7 +1,8 @@
 {
   "Action": "assemble",
-  "PlanProtocol": "v1",
-  "PlanGcsUri": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/plan.tar.gz",
+  "PlanV2ManifestGcsUri": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/v2/manifest.json",
+  "PlanV2ArtifactGcsPrefix": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/v2/artifacts/sha256",
+  "PlanHash": "REPLACE_WITH_PLAN_HASH",
   "ChunkGcsUris": [
     "gs://hyperframes-render-PROJECT/renders/hf-render-demo/chunks/0000.mp4",
     "gs://hyperframes-render-PROJECT/renders/hf-render-demo/chunks/0001.mp4"
diff --git a/examples/gcp-cloud-run/sample-events/plan-v1.json b/examples/gcp-cloud-run/sample-events/plan-v1.json
new file mode 100644
index 000000000..6f0856668
--- /dev/null
+++ b/examples/gcp-cloud-run/sample-events/plan-v1.json
@@ -0,0 +1,7 @@
+{
+  "Action": "plan",
+  "PlanProtocol": "v1",
+  "ProjectGcsUri": "gs://hyperframes-render-PROJECT/sites/abc123/project.tar.gz",
+  "PlanOutputGcsPrefix": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/",
+  "Config": { "fps": 30, "width": 1920, "height": 1080, "format": "mp4" }
+}
diff --git a/examples/gcp-cloud-run/sample-events/plan.json b/examples/gcp-cloud-run/sample-events/plan.json
index 6f0856668..667988b41 100644
--- a/examples/gcp-cloud-run/sample-events/plan.json
+++ b/examples/gcp-cloud-run/sample-events/plan.json
@@ -1,6 +1,5 @@
 {
   "Action": "plan",
-  "PlanProtocol": "v1",
   "ProjectGcsUri": "gs://hyperframes-render-PROJECT/sites/abc123/project.tar.gz",
   "PlanOutputGcsPrefix": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/",
   "Config": { "fps": 30, "width": 1920, "height": 1080, "format": "mp4" }
diff --git a/examples/gcp-cloud-run/sample-events/render-chunk-v1.json b/examples/gcp-cloud-run/sample-events/render-chunk-v1.json
new file mode 100644
index 000000000..c11bd441a
--- /dev/null
+++ b/examples/gcp-cloud-run/sample-events/render-chunk-v1.json
@@ -0,0 +1,9 @@
+{
+  "Action": "renderChunk",
+  "PlanProtocol": "v1",
+  "PlanGcsUri": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/plan.tar.gz",
+  "PlanHash": "REPLACE_WITH_PLAN_HASH",
+  "ChunkIndex": 0,
+  "ChunkOutputGcsPrefix": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/",
+  "Format": "mp4"
+}
diff --git a/examples/gcp-cloud-run/sample-events/render-chunk.json b/examples/gcp-cloud-run/sample-events/render-chunk.json
index c11bd441a..cbc3c8be0 100644
--- a/examples/gcp-cloud-run/sample-events/render-chunk.json
+++ b/examples/gcp-cloud-run/sample-events/render-chunk.json
@@ -1,7 +1,7 @@
 {
   "Action": "renderChunk",
-  "PlanProtocol": "v1",
-  "PlanGcsUri": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/plan.tar.gz",
+  "PlanV2ManifestGcsUri": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/v2/manifest.json",
+  "PlanV2ArtifactGcsPrefix": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/v2/artifacts/sha256",
   "PlanHash": "REPLACE_WITH_PLAN_HASH",
   "ChunkIndex": 0,
   "ChunkOutputGcsPrefix": "gs://hyperframes-render-PROJECT/renders/hf-render-demo/",
diff --git a/examples/gcp-cloud-run/scripts/smoke.sh b/examples/gcp-cloud-run/scripts/smoke.sh
index 91a4d4d58..669b82621 100755
--- a/examples/gcp-cloud-run/scripts/smoke.sh
+++ b/examples/gcp-cloud-run/scripts/smoke.sh
@@ -2,11 +2,11 @@
 # Owner-isolated real-GCP smoke + v1/v2 parity test for the HyperFrames
 # Cloud Run adapter.
 #
-# The default is intentionally v1-only. Plan protocol v2 must be opted into
-# explicitly with --protocols v1,v2. Every invocation derives a unique,
-# length-safe resource prefix and uses an isolated Terraform working directory
-# and state file. Cleanup verifies every owned resource is absent and fails
-# closed on API/authentication errors.
+# The default exercises Plan v2. Deprecated v1 compatibility can be selected
+# explicitly with --protocols v1 or compared with --protocols v1,v2. Every
+# invocation derives a unique, length-safe resource prefix and uses an isolated
+# Terraform working directory and state file. Cleanup verifies every owned
+# resource is absent and fails closed on API/authentication errors.
 #
 # Usage:
 #   ./smoke.sh --project <gcp-project>
@@ -33,7 +33,7 @@ REGION="${GCP_REGION:-us-central1}"
 FIXTURE="${FIXTURE:-mp4-h264-sdr}"
 CHUNK_SIZES="${CHUNK_SIZES:-}"
 PSNR_THRESHOLD="${PSNR_THRESHOLD:-35}"
-PROTOCOLS="${PROTOCOLS:-v1}"
+PROTOCOLS="${PROTOCOLS:-v2}"
 OWNER="${HYPERFRAMES_SMOKE_OWNER:-}"
 AR_REPO="${AR_REPO:-}"
 AR_REPO_WAS_EXPLICIT=0
diff --git a/packages/aws-lambda/README.md b/packages/aws-lambda/README.md
index 14423f08e..0ef9a34cb 100644
--- a/packages/aws-lambda/README.md
+++ b/packages/aws-lambda/README.md
@@ -47,14 +47,13 @@ inside Step Functions' history budget (under 200 bytes per chunk).
 
 ### Plan transport selection
 
-Plan v2 is recommended for new integrations. `renderToLambda` still defaults
-an omitted `planProtocol` to the existing monolithic v1 transport for
-backwards compatibility, so select v2 explicitly:
+Plan v2 is the default for new renders. When `planProtocol` is omitted,
+`renderToLambda` sends an explicit `PlanProtocol: "v2"` so the SDK and the
+deployed state machine agree:
 
 ```ts
 await renderToLambda({
   // ...bucket, state machine, project, and config...
-  planProtocol: "v2",
 });
 ```
 
@@ -64,7 +63,24 @@ only manifest-selected chunk artifacts, while the assembler fetches its
 own metadata and audio subset. Blobs are immutable SHA-256-addressed
 objects, verified on upload and download, and the manifest is published
 last. Unknown protocols and digest mismatches are terminal Step Functions
-errors. Omit the selector—or use `"v1"`—to retain the prior wire contract.
+errors. The monolithic v1 transport remains available as deprecated
+compatibility by passing `planProtocol: "v1"` explicitly.
+
+#### Upgrade order
+
+This default changes application behavior and requires a coordinated
+infrastructure upgrade. Before upgrading an application that calls
+`renderToLambda`:
+
+1. Pause new renders and let existing Step Functions executions drain.
+2. Redeploy the Lambda handler and SAM template or CDK construct from the
+   same new package version.
+3. Resume renders, then upgrade the application/SDK dependency.
+
+Older state machines can default missing protocol fields to v1 or lack v2
+branches, while the new SDK sends explicit v2. If infrastructure cannot be
+redeployed first, keep the application on its previous package version or
+pass `planProtocol: "v1"` explicitly until the redeploy is complete.
 
 ## Chrome runtime
 
diff --git a/packages/aws-lambda/src/cdk/HyperframesRenderStack.snapshot.test.ts b/packages/aws-lambda/src/cdk/HyperframesRenderStack.snapshot.test.ts
index c7f27f503..010a0d2c3 100644
--- a/packages/aws-lambda/src/cdk/HyperframesRenderStack.snapshot.test.ts
+++ b/packages/aws-lambda/src/cdk/HyperframesRenderStack.snapshot.test.ts
@@ -151,6 +151,18 @@ describe("HyperframesRenderStack — snapshot", () => {
     expect(actualStates.sort()).toEqual([...EXPECTED_STATE_NAMES].sort());
   });
 
+  it("defaults omitted plan protocol to v2 and preserves the explicit v1 branch", () => {
+    for (const definition of [SYNTHED.definition, readSamDefinition()]) {
+      const selection = requireRecord(
+        definition.States.SelectPlanProtocol,
+        "SelectPlanProtocol state",
+      );
+      expect(selection.Default).toBe("PlanV2");
+      expect(JSON.stringify(selection)).toContain('"StringEquals":"v1"');
+      expect(JSON.stringify(definition.States.Plan)).toContain('"PlanProtocol":"v1"');
+    }
+  });
+
   it("preserves every typed non-retryable error name across the three Lambda tasks", () => {
     const { definition } = SYNTHED;
     const collected = new Set<string>();
diff --git a/packages/aws-lambda/src/cdk/HyperframesRenderStack.ts b/packages/aws-lambda/src/cdk/HyperframesRenderStack.ts
index baa7bd6b1..8b0c4a7a1 100644
--- a/packages/aws-lambda/src/cdk/HyperframesRenderStack.ts
+++ b/packages/aws-lambda/src/cdk/HyperframesRenderStack.ts
@@ -247,6 +247,7 @@ export class HyperframesRenderStack extends Construct {
       lambdaFunction: this.renderFunction,
       payload: sfn.TaskInput.fromObject({
         Action: "plan",
+        PlanProtocol: "v1",
         "ProjectS3Uri.$": "$.ProjectS3Uri",
         "PlanOutputS3Prefix.$": "$.PlanOutputS3Prefix",
         "Config.$": "$.Config",
@@ -319,6 +320,7 @@ export class HyperframesRenderStack extends Construct {
       lambdaFunction: this.renderFunction,
       payload: sfn.TaskInput.fromObject({
         Action: "renderChunk",
+        PlanProtocol: "v1",
         "ChunkIndex.$": "$.ChunkIndex",
         "PlanS3Uri.$": "$.PlanS3Uri",
         "PlanHash.$": "$.PlanHash",
@@ -361,6 +363,7 @@ export class HyperframesRenderStack extends Construct {
       lambdaFunction: this.renderFunction,
       payload: sfn.TaskInput.fromObject({
         Action: "assemble",
+        PlanProtocol: "v1",
         "PlanS3Uri.$": "$.Plan.PlanS3Uri",
         "ChunkS3Uris.$": "$.Chunks[*].ChunkS3Uri",
         "AudioS3Uri.$": "$.Plan.AudioS3Uri",
@@ -473,13 +476,13 @@ export class HyperframesRenderStack extends Construct {
 
     const unsupportedPlanProtocol = new sfn.Fail(this, "UnsupportedPlanProtocol", {
       error: "PLAN_PROTOCOL_UNSUPPORTED",
-      cause: 'PlanProtocol must be "v1", "v2", or absent (defaults to v1).',
+      cause: 'PlanProtocol must be "v1", "v2", or absent (defaults to v2).',
     });
     return new sfn.Choice(this, "SelectPlanProtocol")
       .when(sfn.Condition.stringEquals("$.PlanProtocol", "v2"), planV2)
       .when(sfn.Condition.stringEquals("$.PlanProtocol", "v1"), plan)
       .when(sfn.Condition.isPresent("$.PlanProtocol"), unsupportedPlanProtocol)
-      .otherwise(plan);
+      .otherwise(planV2);
   }
 }
 
diff --git a/packages/aws-lambda/src/events.ts b/packages/aws-lambda/src/events.ts
index 44b5e6066..8b25122dc 100644
--- a/packages/aws-lambda/src/events.ts
+++ b/packages/aws-lambda/src/events.ts
@@ -55,17 +55,17 @@ interface PlanEventBase {
 }
 
 /**
- * Legacy/default plan transport. Absence is deliberately interpreted as v1.
+ * Legacy plan transport. Callers must select it explicitly.
  *
  * @deprecated Use {@link PlanV2Event} for new integrations.
  */
 export interface PlanV1Event extends PlanEventBase {
-  PlanProtocol?: "v1";
+  PlanProtocol: "v1";
 }
 
-/** Explicit opt-in to the content-addressed v2 plan transport. */
+/** Default content-addressed v2 plan transport. */
 export interface PlanV2Event extends PlanEventBase {
-  PlanProtocol: "v2";
+  PlanProtocol?: "v2";
 }
 
 export type PlanEvent = PlanV1Event | PlanV2Event;
@@ -90,12 +90,12 @@ interface RenderChunkEventBase {
 }
 
 /**
- * Legacy/default chunk event.
+ * Legacy chunk event. Callers must select it explicitly.
  *
  * @deprecated Use {@link RenderChunkV2Event} for new integrations.
  */
 export interface RenderChunkV1Event extends RenderChunkEventBase {
-  PlanProtocol?: "v1";
+  PlanProtocol: "v1";
   /** S3 URI of the v1 plan tar produced by a PlanEvent invocation. */
   PlanS3Uri: string;
 }
@@ -105,7 +105,7 @@ export interface RenderChunkV1Event extends RenderChunkEventBase {
  * describes the exact content-addressed artifacts needed by this chunk.
  */
 export interface RenderChunkV2Event extends RenderChunkEventBase {
-  PlanProtocol: "v2";
+  PlanProtocol?: "v2";
   PlanV2ManifestS3Uri: string;
   PlanV2ArtifactS3Prefix: string;
 }
@@ -136,19 +136,19 @@ interface AssembleEventBase {
 }
 
 /**
- * Legacy/default assemble event.
+ * Legacy assemble event. Callers must select it explicitly.
  *
  * @deprecated Use {@link AssembleV2Event} for new integrations.
  */
 export interface AssembleV1Event extends AssembleEventBase {
-  PlanProtocol?: "v1";
+  PlanProtocol: "v1";
   /** S3 URI of the v1 plan tar produced by a PlanEvent invocation. */
   PlanS3Uri: string;
 }
 
 /** V2 assemble event, scoped to manifest-declared assembler artifacts. */
 export interface AssembleV2Event extends AssembleEventBase {
-  PlanProtocol: "v2";
+  PlanProtocol?: "v2";
   PlanV2ManifestS3Uri: string;
   PlanV2ArtifactS3Prefix: string;
   PlanHash: string;
diff --git a/packages/aws-lambda/src/handler.test.ts b/packages/aws-lambda/src/handler.test.ts
index d1af1a96d..ec8a3d540 100644
--- a/packages/aws-lambda/src/handler.test.ts
+++ b/packages/aws-lambda/src/handler.test.ts
@@ -145,6 +145,7 @@ describe("unwrapEvent", () => {
   it("unwraps a Step Functions { Payload } envelope", () => {
     const inner: RenderChunkEvent = {
       Action: "renderChunk",
+      PlanProtocol: "v1",
       PlanS3Uri: "s3://bucket/plan.tar.gz",
       PlanHash: "deadbeef",
       ChunkIndex: 3,
@@ -158,6 +159,7 @@ describe("unwrapEvent", () => {
   it("unwraps multiple levels of envelopes", () => {
     const inner: AssembleEvent = {
       Action: "assemble",
+      PlanProtocol: "v1",
       PlanS3Uri: "s3://bucket/plan.tar.gz",
       ChunkS3Uris: ["s3://bucket/chunks/0001.mp4"],
       AudioS3Uri: null,
@@ -176,7 +178,7 @@ describe("unwrapEvent", () => {
 });
 
 describe("handler dispatch", () => {
-  it("routes Action='plan' to the plan primitive", async () => {
+  it("preserves explicit v1 plan compatibility", async () => {
     const tmpRoot = makeTmpRoot();
     const s3 = new FakeS3Client();
     // Seed a fake project tarball so the untar step has something to chew on.
@@ -213,6 +215,7 @@ describe("handler dispatch", () => {
 
     const event: PlanEvent = {
       Action: "plan",
+      PlanProtocol: "v1",
       ProjectS3Uri: "s3://bucket/project.tar.gz",
       PlanOutputS3Prefix: "s3://bucket/renders/abc/",
       Config: { fps: 30, width: 1920, height: 1080, format: "mp4" },
@@ -270,6 +273,7 @@ describe("handler dispatch", () => {
         handler(
           {
             Action: "plan",
+            PlanProtocol: "v1",
             ProjectS3Uri: "s3://bucket/project.tar.gz",
             PlanOutputS3Prefix: "s3://bucket/renders/terminal/",
             Config: { fps: 30, width: 640, height: 360, format: "mp4" },
@@ -332,6 +336,7 @@ describe("handler dispatch", () => {
 
     const event: PlanEvent = {
       Action: "plan",
+      PlanProtocol: "v1",
       ProjectS3Uri: "s3://bucket/project.tar.gz",
       PlanOutputS3Prefix: "s3://bucket/renders/abc/",
       Config: { fps: 30, width: 1920, height: 1080, format: "mp4" },
@@ -406,6 +411,7 @@ describe("handler dispatch", () => {
 
     const event: RenderChunkEvent = {
       Action: "renderChunk",
+      PlanProtocol: "v1",
       PlanS3Uri: "s3://bucket/plan.tar.gz",
       PlanHash: "fakehash",
       ChunkIndex: 2,
@@ -455,6 +461,7 @@ describe("handler dispatch", () => {
 
     const event: RenderChunkEvent = {
       Action: "renderChunk",
+      PlanProtocol: "v1",
       PlanS3Uri: "s3://bucket/plan.tar.gz",
       PlanHash: "not-the-real-hash",
       ChunkIndex: 0,
@@ -511,6 +518,7 @@ describe("handler dispatch", () => {
 
     const event: AssembleEvent = {
       Action: "assemble",
+      PlanProtocol: "v1",
       PlanS3Uri: "s3://bucket/plan.tar.gz",
       ChunkS3Uris: ["s3://bucket/chunks/0001.mp4", "s3://bucket/chunks/0002.mp4"],
       AudioS3Uri: null,
@@ -541,7 +549,7 @@ describe("handler dispatch", () => {
     expect(assembleMock).toHaveBeenCalledTimes(1);
   });
 
-  it("runs v2 plan → target-scoped chunk → assemble without a PlanS3Uri", async () => {
+  it("defaults omitted plan protocol to v2 across plan → chunk → assemble", async () => {
     const tmpRoot = makeTmpRoot();
     const s3 = new FakeS3Client();
     s3.objects.set("s3://bucket/project.tar.gz", await makeMinimalProjectTar());
@@ -614,7 +622,6 @@ describe("handler dispatch", () => {
     const planned = await handler(
       {
         Action: "plan",
-        PlanProtocol: "v2",
         ProjectS3Uri: "s3://bucket/project.tar.gz",
         PlanOutputS3Prefix: "s3://bucket/renders/v2/",
         Config: { fps: 30, width: 640, height: 360, format: "mp4" },
@@ -642,7 +649,6 @@ describe("handler dispatch", () => {
     const chunk = await handler(
       {
         Action: "renderChunk",
-        PlanProtocol: "v2",
         PlanV2ManifestS3Uri: planned.PlanV2ManifestS3Uri,
         PlanV2ArtifactS3Prefix: planned.PlanV2ArtifactS3Prefix,
         PlanHash: planned.PlanHash,
@@ -661,7 +667,6 @@ describe("handler dispatch", () => {
     await handler(
       {
         Action: "assemble",
-        PlanProtocol: "v2",
         PlanV2ManifestS3Uri: planned.PlanV2ManifestS3Uri,
         PlanV2ArtifactS3Prefix: planned.PlanV2ArtifactS3Prefix,
         PlanHash: planned.PlanHash,
@@ -677,6 +682,56 @@ describe("handler dispatch", () => {
     ).toBe(true);
   });
 
+  it("rejects unknown plan protocol values", async () => {
+    const tmpRoot = makeTmpRoot();
+    const s3 = new FakeS3Client();
+
+    await expect(
+      handler(
+        {
+          Action: "plan",
+          PlanProtocol: "v3",
+          ProjectS3Uri: "s3://bucket/project.tar.gz",
+          PlanOutputS3Prefix: "s3://bucket/renders/invalid/",
+          Config: { fps: 30, width: 640, height: 360, format: "mp4" },
+        } as unknown as LambdaEvent,
+        {
+          s3: s3 as unknown as import("@aws-sdk/client-s3").S3Client,
+          tmpRoot,
+          skipChromeResolution: true,
+        },
+      ),
+    ).rejects.toMatchObject({ name: "PLAN_PROTOCOL_UNSUPPORTED" });
+    expect(s3.ops).toHaveLength(0);
+  });
+
+  it("rejects mixed v1/v2 plan locators at runtime", async () => {
+    const tmpRoot = makeTmpRoot();
+    const s3 = new FakeS3Client();
+
+    await expect(
+      handler(
+        {
+          Action: "renderChunk",
+          PlanS3Uri: "s3://bucket/plan.tar.gz",
+          PlanHash: "fakehash",
+          ChunkIndex: 0,
+          ChunkOutputS3Prefix: "s3://bucket/renders/mixed/",
+          Format: "mp4",
+        } as unknown as LambdaEvent,
+        {
+          s3: s3 as unknown as import("@aws-sdk/client-s3").S3Client,
+          tmpRoot,
+          skipChromeResolution: true,
+        },
+      ),
+    ).rejects.toMatchObject({
+      name: "PLAN_PROTOCOL_UNSUPPORTED",
+      message: expect.stringContaining("mixed or missing plan locators"),
+    });
+    expect(s3.ops).toHaveLength(0);
+  });
+
   it("rejects unknown actions", async () => {
     const tmpRoot = makeTmpRoot();
     await expect(
@@ -735,6 +790,7 @@ describe("handler — S3 URI allowlist (security: F-004)", () => {
 
     const event: AssembleEvent = {
       Action: "assemble",
+      PlanProtocol: "v1",
       PlanS3Uri: "s3://good-bucket/plan.tar.gz",
       ChunkS3Uris: ["s3://good-bucket/chunks/0001.mp4", "s3://evil-bucket/chunks/0002.mp4"],
       AudioS3Uri: null,
diff --git a/packages/aws-lambda/src/handler.ts b/packages/aws-lambda/src/handler.ts
index e16b68b78..08fc2caf3 100644
--- a/packages/aws-lambda/src/handler.ts
+++ b/packages/aws-lambda/src/handler.ts
@@ -44,9 +44,12 @@ import type {
   LambdaEvent,
   LambdaResult,
   PlanEvent,
+  PlanV2Event,
   PlanLambdaResult,
   RenderChunkEvent,
+  RenderChunkV2Event,
   RenderChunkLambdaResult,
+  AssembleV2Event,
 } from "./events.js";
 import {
   downloadS3ObjectToFile,
@@ -97,6 +100,7 @@ export interface HandlerDeps {
  */
 export async function handler(event: LambdaEvent, deps?: HandlerDeps): Promise<LambdaResult> {
   const unwrapped = unwrapEvent(event);
+  validatePlanProtocolShape(unwrapped);
   validateEventS3Uris(unwrapped);
   primeRuntimeEnv();
   // Single structured boot log line — CloudWatch Logs Insights queries
@@ -201,6 +205,43 @@ function isLambdaAction(value: string): value is LambdaAction {
   return value === "plan" || value === "renderChunk" || value === "assemble";
 }
 
+// This is the single fail-closed boundary for the wire union. Keeping all
+// forbidden locator combinations together makes mixed-protocol input auditable.
+// fallow-ignore-next-line complexity
+function validatePlanProtocolShape(event: PlanEvent | RenderChunkEvent | AssembleEvent): void {
+  const raw = event as unknown as Record<string, unknown>;
+  const protocol = raw.PlanProtocol;
+  if (protocol !== undefined && protocol !== "v1" && protocol !== "v2") {
+    const error = new Error(
+      `[handler] unsupported PlanProtocol ${JSON.stringify(protocol)}; expected "v1", "v2", or absent`,
+    );
+    error.name = "PLAN_PROTOCOL_UNSUPPORTED";
+    throw error;
+  }
+  if (event.Action === "plan") return;
+
+  const effectiveProtocol = protocol ?? "v2";
+  const hasV1Locator = typeof raw.PlanS3Uri === "string";
+  const hasV2Manifest = typeof raw.PlanV2ManifestS3Uri === "string";
+  const hasV2Prefix = typeof raw.PlanV2ArtifactS3Prefix === "string";
+  const valid =
+    effectiveProtocol === "v2"
+      ? !hasV1Locator && hasV2Manifest && hasV2Prefix
+      : hasV1Locator && !hasV2Manifest && !hasV2Prefix;
+  if (!valid) {
+    const error = new Error(
+      `[handler] ${effectiveProtocol} ${event.Action} event has mixed or missing plan locators`,
+    );
+    error.name = "PLAN_PROTOCOL_UNSUPPORTED";
+    throw error;
+  }
+  if (effectiveProtocol === "v2" && event.Action === "assemble" && event.AudioS3Uri !== null) {
+    const error = new Error("[handler] v2 assemble audio must be materialized from the manifest");
+    error.name = "PLAN_PROTOCOL_UNSUPPORTED";
+    throw error;
+  }
+}
+
 /**
  * Emit a single JSON line to stdout. CloudWatch ingests each line as a
  * structured event; Logs Insights queries can `filter event="..."` and
@@ -229,14 +270,14 @@ function summarizeEvent(
       return {
         projectS3Uri: event.ProjectS3Uri,
         planOutputS3Prefix: event.PlanOutputS3Prefix,
-        planProtocol: event.PlanProtocol ?? "v1",
+        planProtocol: event.PlanProtocol ?? "v2",
         format: event.Config.format,
         fps: event.Config.fps,
       };
     case "renderChunk":
       return {
-        planProtocol: event.PlanProtocol ?? "v1",
-        ...(event.PlanProtocol === "v2"
+        planProtocol: event.PlanProtocol ?? "v2",
+        ...(event.PlanProtocol !== "v1"
           ? { planV2ManifestS3Uri: event.PlanV2ManifestS3Uri }
           : { planS3Uri: event.PlanS3Uri }),
         chunkIndex: event.ChunkIndex,
@@ -244,8 +285,8 @@ function summarizeEvent(
       };
     case "assemble":
       return {
-        planProtocol: event.PlanProtocol ?? "v1",
-        ...(event.PlanProtocol === "v2"
+        planProtocol: event.PlanProtocol ?? "v2",
+        ...(event.PlanProtocol !== "v1"
           ? { planV2ManifestS3Uri: event.PlanV2ManifestS3Uri }
           : { planS3Uri: event.PlanS3Uri }),
         chunkCount: event.ChunkS3Uris.length,
@@ -278,7 +319,7 @@ function primeRuntimeEnv(): void {
 // The v1 handler owns one transactional download, plan, archive, upload, and cleanup lifecycle.
 // fallow-ignore-next-line complexity
 async function handlePlan(event: PlanEvent, deps?: HandlerDeps): Promise<PlanLambdaResult> {
-  if (event.PlanProtocol === "v2") {
+  if (event.PlanProtocol !== "v1") {
     return handlePlanV2(event, deps);
   }
   const started = Date.now();
@@ -358,7 +399,7 @@ async function handlePlan(event: PlanEvent, deps?: HandlerDeps): Promise<PlanLam
 // and manifest-last publication must stay ordered and fail together.
 // fallow-ignore-next-line complexity
 async function handlePlanV2(
-  event: Extract<PlanEvent, { PlanProtocol: "v2" }>,
+  event: PlanV2Event,
   deps?: HandlerDeps,
 ): Promise<Extract<PlanLambdaResult, { PlanProtocol: "v2" }>> {
   const started = Date.now();
@@ -412,7 +453,7 @@ async function handleRenderChunk(
   event: RenderChunkEvent,
   deps?: HandlerDeps,
 ): Promise<RenderChunkLambdaResult> {
-  if (event.PlanProtocol === "v2") {
+  if (event.PlanProtocol !== "v1") {
     return handleRenderChunkV2(event, deps);
   }
   const started = Date.now();
@@ -481,7 +522,7 @@ async function handleRenderChunk(
 // render, and upload in one lifecycle so cleanup and errors remain atomic.
 // fallow-ignore-next-line complexity
 async function handleRenderChunkV2(
-  event: Extract<RenderChunkEvent, { PlanProtocol: "v2" }>,
+  event: RenderChunkV2Event,
   deps?: HandlerDeps,
 ): Promise<RenderChunkLambdaResult> {
   const started = Date.now();
@@ -554,7 +595,7 @@ async function handleAssemble(
   event: AssembleEvent,
   deps?: HandlerDeps,
 ): Promise<AssembleLambdaResult> {
-  if (event.PlanProtocol === "v2") {
+  if (event.PlanProtocol !== "v1") {
     return handleAssembleV2(event, deps);
   }
   const started = Date.now();
@@ -610,7 +651,7 @@ async function handleAssemble(
 // keeping the steps local makes its temporary-storage ownership explicit.
 // fallow-ignore-next-line complexity
 async function handleAssembleV2(
-  event: Extract<AssembleEvent, { PlanProtocol: "v2" }>,
+  event: AssembleV2Event,
   deps?: HandlerDeps,
 ): Promise<AssembleLambdaResult> {
   const started = Date.now();
@@ -776,12 +817,12 @@ function getEventS3Uris(event: PlanEvent | RenderChunkEvent | AssembleEvent): st
     case "plan":
       return [event.ProjectS3Uri, event.PlanOutputS3Prefix];
     case "renderChunk":
-      return event.PlanProtocol === "v2"
+      return event.PlanProtocol !== "v1"
         ? [event.PlanV2ManifestS3Uri, event.PlanV2ArtifactS3Prefix, event.ChunkOutputS3Prefix]
         : [event.PlanS3Uri, event.ChunkOutputS3Prefix];
     case "assemble":
       return [
-        ...(event.PlanProtocol === "v2"
+        ...(event.PlanProtocol !== "v1"
           ? [event.PlanV2ManifestS3Uri, event.PlanV2ArtifactS3Prefix]
           : [event.PlanS3Uri]),
         ...event.ChunkS3Uris,
diff --git a/packages/aws-lambda/src/sdk/renderToLambda.test.ts b/packages/aws-lambda/src/sdk/renderToLambda.test.ts
index 61402c2ad..bb9007bb0 100644
--- a/packages/aws-lambda/src/sdk/renderToLambda.test.ts
+++ b/packages/aws-lambda/src/sdk/renderToLambda.test.ts
@@ -98,11 +98,11 @@ describe("renderToLambda", () => {
       PlanOutputS3Prefix: "s3://test-bucket/renders/smoke-1/",
       OutputS3Uri: "s3://test-bucket/renders/smoke-1/output.mp4",
       Config: baseConfig,
-      PlanProtocol: "v1",
+      PlanProtocol: "v2",
     });
   });
 
-  it("opts the complete execution into plan protocol v2 explicitly", async () => {
+  it("preserves explicit plan protocol v1 compatibility", async () => {
     const sfn = new FakeSFN();
     const s3 = new FakeS3();
     const handle = await renderToLambda({
@@ -110,18 +110,18 @@ describe("renderToLambda", () => {
       bucketName: "test-bucket",
       stateMachineArn: "arn:aws:states:us-east-1:1234:stateMachine:hf",
       config: baseConfig,
-      executionName: "smoke-v2",
-      planProtocol: "v2",
+      executionName: "smoke-v1",
+      planProtocol: "v1",
       sfn: asSFNClient(sfn),
       s3: asS3Client(s3),
     });
 
     expect(sfn.starts[0]?.input).toEqual({
       ProjectS3Uri: handle.projectS3Uri,
-      PlanOutputS3Prefix: "s3://test-bucket/renders/smoke-v2/",
-      OutputS3Uri: "s3://test-bucket/renders/smoke-v2/output.mp4",
+      PlanOutputS3Prefix: "s3://test-bucket/renders/smoke-v1/",
+      OutputS3Uri: "s3://test-bucket/renders/smoke-v1/output.mp4",
       Config: baseConfig,
-      PlanProtocol: "v2",
+      PlanProtocol: "v1",
     });
   });
 
diff --git a/packages/aws-lambda/src/sdk/renderToLambda.ts b/packages/aws-lambda/src/sdk/renderToLambda.ts
index 8df5e20c1..1232e6876 100644
--- a/packages/aws-lambda/src/sdk/renderToLambda.ts
+++ b/packages/aws-lambda/src/sdk/renderToLambda.ts
@@ -38,8 +38,8 @@ export interface RenderToLambdaOptions {
   /** Validated `SerializableDistributedRenderConfig` (no logger / abortSignal). */
   config: SerializableDistributedRenderConfig;
   /**
-   * Distributed plan transport. Defaults to `"v1"` for backwards
-   * compatibility. New integrations should explicitly select `"v2"`.
+   * Distributed plan transport. Defaults to `"v2"`. Select `"v1"`
+   * explicitly only for deprecated compatibility with the monolithic plan.
    */
   planProtocol?: LambdaPlanProtocol;
   /** S3 bucket from the SAM stack output (`RenderBucketName`). */
@@ -115,7 +115,7 @@ export async function renderToLambda(opts: RenderToLambdaOptions): Promise<Rende
     PlanOutputS3Prefix: planOutputS3Prefix,
     OutputS3Uri: outputS3Uri,
     Config: opts.config,
-    PlanProtocol: opts.planProtocol ?? "v1",
+    PlanProtocol: opts.planProtocol ?? "v2",
   };
 
   // Reject oversize input client-side. Step Functions Standard caps the
diff --git a/packages/gcp-cloud-run/README.md b/packages/gcp-cloud-run/README.md
index aa9c8c3ca..9af2f6a24 100644
--- a/packages/gcp-cloud-run/README.md
+++ b/packages/gcp-cloud-run/README.md
@@ -45,14 +45,13 @@ per-step durations on success.
 
 ### Plan transport selection
 
-Plan v2 is recommended for new integrations. `renderToCloudRun` still
-interprets an omitted `planProtocol` as `"v1"` for backwards compatibility,
-so new callers should select v2 explicitly:
+Plan v2 is the default for new renders. When `planProtocol` is omitted,
+`renderToCloudRun` sends an explicit `PlanProtocol: "v2"` so the SDK and
+the deployed workflow agree:
 
 ```ts
 await renderToCloudRun({
   // ...project, bucket, workflow, service, and config...
-  planProtocol: "v2",
 });
 ```
 
@@ -60,6 +59,20 @@ V2 uses separate manifest and content-addressed artifact locators throughout
 the workflow. Unknown protocols and integrity failures fail closed; a render
 never mixes v1 and v2 artifacts.
 
+The monolithic v1 transport remains available as deprecated compatibility by
+passing `planProtocol: "v1"` explicitly.
+
+#### Upgrade order
+
+Redeploy the Cloud Run image and Cloud Workflows definition from the same new
+package version before upgrading an application that calls
+`renderToCloudRun`. Pause new renders and drain active workflow executions
+during the infrastructure update. Older workflows can default omission to v1
+or lack the v2 branch, while the new SDK sends explicit v2. If infrastructure
+cannot be redeployed first, keep the previous SDK version or pass
+`planProtocol: "v1"` explicitly until the Terraform/workflow redeploy is
+complete.
+
 ## Chrome runtime
 
 Unlike the Lambda adapter — which fights a 250 MB ZIP ceiling and
diff --git a/packages/gcp-cloud-run/src/events.ts b/packages/gcp-cloud-run/src/events.ts
index 8cc7ef469..244b03292 100644
--- a/packages/gcp-cloud-run/src/events.ts
+++ b/packages/gcp-cloud-run/src/events.ts
@@ -61,17 +61,17 @@ interface PlanEventBase {
 }
 
 /**
- * Legacy/default plan transport. Absence is deliberately interpreted as v1.
+ * Legacy plan transport. Callers must select it explicitly.
  *
  * @deprecated Use {@link PlanV2Event} for new integrations.
  */
 export interface PlanV1Event extends PlanEventBase {
-  PlanProtocol?: "v1";
+  PlanProtocol: "v1";
 }
 
-/** Explicit opt-in to the content-addressed v2 plan transport. */
+/** Default content-addressed v2 plan transport. */
 export interface PlanV2Event extends PlanEventBase {
-  PlanProtocol: "v2";
+  PlanProtocol?: "v2";
 }
 
 export type PlanEvent = PlanV1Event | PlanV2Event;
@@ -96,12 +96,12 @@ interface RenderChunkEventBase {
 }
 
 /**
- * Legacy/default chunk event.
+ * Legacy chunk event. Callers must select it explicitly.
  *
  * @deprecated Use {@link RenderChunkV2Event} for new integrations.
  */
 export interface RenderChunkV1Event extends RenderChunkEventBase {
-  PlanProtocol?: "v1";
+  PlanProtocol: "v1";
   /** GCS URI of the v1 plan tar produced by a PlanEvent invocation. */
   PlanGcsUri: string;
   PlanV2ManifestGcsUri?: never;
@@ -113,7 +113,7 @@ export interface RenderChunkV1Event extends RenderChunkEventBase {
  * describes the exact content-addressed artifacts needed by this chunk.
  */
 export interface RenderChunkV2Event extends RenderChunkEventBase {
-  PlanProtocol: "v2";
+  PlanProtocol?: "v2";
   PlanV2ManifestGcsUri: string;
   PlanV2ArtifactGcsPrefix: string;
   PlanGcsUri?: never;
@@ -143,12 +143,12 @@ interface AssembleEventBase {
 }
 
 /**
- * Legacy/default assemble event.
+ * Legacy assemble event. Callers must select it explicitly.
  *
  * @deprecated Use {@link AssembleV2Event} for new integrations.
  */
 export interface AssembleV1Event extends AssembleEventBase {
-  PlanProtocol?: "v1";
+  PlanProtocol: "v1";
   /** GCS URI of the v1 plan tar produced by a PlanEvent invocation. */
   PlanGcsUri: string;
   /** Legacy standalone audio locator; `null` when audio is embedded in the v1 plan tar. */
@@ -159,7 +159,7 @@ export interface AssembleV1Event extends AssembleEventBase {
 
 /** V2 assemble event, scoped to manifest-declared assembler artifacts. */
 export interface AssembleV2Event extends AssembleEventBase {
-  PlanProtocol: "v2";
+  PlanProtocol?: "v2";
   PlanV2ManifestGcsUri: string;
   PlanV2ArtifactGcsPrefix: string;
   PlanHash: string;
diff --git a/packages/gcp-cloud-run/src/sdk/renderToCloudRun.test.ts b/packages/gcp-cloud-run/src/sdk/renderToCloudRun.test.ts
index 6cf716892..cc487a991 100644
--- a/packages/gcp-cloud-run/src/sdk/renderToCloudRun.test.ts
+++ b/packages/gcp-cloud-run/src/sdk/renderToCloudRun.test.ts
@@ -88,16 +88,16 @@ describe("renderToCloudRun", () => {
       OutputGcsUri: "gs://b/renders/hf-render-fixed/output.mp4",
       ServiceUrl: "https://render-abc.run.app",
       Config: config,
-      PlanProtocol: "v1",
+      PlanProtocol: "v2",
     });
     expect(fake.lastParent).toBe(
       "projects/proj/locations/us-central1/workflows/hyperframes-render",
     );
   });
 
-  it("forwards an explicit v2 whole-render opt-in", async () => {
+  it("preserves explicit plan protocol v1 compatibility", async () => {
     const fake = new FakeExecutions();
-    await renderToCloudRun({ ...opts(fake), planProtocol: "v2" });
+    await renderToCloudRun({ ...opts(fake), planProtocol: "v1" });
     const arg = JSON.parse(fake.lastArgument ?? "{}");
     expect(arg).toEqual({
       RenderId: "hf-render-fixed",
@@ -106,7 +106,7 @@ describe("renderToCloudRun", () => {
       OutputGcsUri: "gs://b/renders/hf-render-fixed/output.mp4",
       ServiceUrl: "https://render-abc.run.app",
       Config: config,
-      PlanProtocol: "v2",
+      PlanProtocol: "v1",
     });
   });
 
diff --git a/packages/gcp-cloud-run/src/sdk/renderToCloudRun.ts b/packages/gcp-cloud-run/src/sdk/renderToCloudRun.ts
index ae07d2e91..55cb20a3c 100644
--- a/packages/gcp-cloud-run/src/sdk/renderToCloudRun.ts
+++ b/packages/gcp-cloud-run/src/sdk/renderToCloudRun.ts
@@ -53,8 +53,8 @@ export interface RenderToCloudRunOptions {
   /** Validated `SerializableDistributedRenderConfig` (no logger / abortSignal). */
   config: SerializableDistributedRenderConfig;
   /**
-   * Distributed plan transport. Defaults to `"v1"` for backwards
-   * compatibility. New integrations should explicitly select `"v2"`.
+   * Distributed plan transport. Defaults to `"v2"`. Select `"v1"`
+   * explicitly only for deprecated compatibility with the monolithic plan.
    */
   planProtocol?: CloudRunPlanProtocol;
   /** GCS bucket from the Terraform output (`render_bucket_name`). */
@@ -149,7 +149,7 @@ export async function renderToCloudRun(opts: RenderToCloudRunOptions): Promise<R
     OutputGcsUri: outputGcsUri,
     ServiceUrl: opts.serviceUrl,
     Config: opts.config,
-    PlanProtocol: opts.planProtocol ?? "v1",
+    PlanProtocol: opts.planProtocol ?? "v2",
   };
 
   // Reject oversize input client-side. Cloud Workflows caps the execution
diff --git a/packages/gcp-cloud-run/src/server.test.ts b/packages/gcp-cloud-run/src/server.test.ts
index 691dc82fb..143c690c7 100644
--- a/packages/gcp-cloud-run/src/server.test.ts
+++ b/packages/gcp-cloud-run/src/server.test.ts
@@ -178,11 +178,12 @@ describe("unwrapEvent", () => {
 });
 
 describe("dispatch", () => {
-  it("routes plan, uploads the plan tarball", async () => {
+  it("preserves explicit v1 plan compatibility", async () => {
     const gcs = new FakeGcs();
     await seedProjectTar(gcs, "gs://b/sites/x/project.tar.gz");
     const event: PlanEvent = {
       Action: "plan",
+      PlanProtocol: "v1",
       ProjectGcsUri: "gs://b/sites/x/project.tar.gz",
       PlanOutputGcsPrefix: "gs://b/renders/r1/",
       Config: { fps: 30, width: 1920, height: 1080, format: "mp4" } as PlanEvent["Config"],
@@ -201,6 +202,7 @@ describe("dispatch", () => {
     await seedPlanTar(gcs, "gs://b/renders/r1/plan.tar.gz", PLAN_HASH);
     const event: RenderChunkEvent = {
       Action: "renderChunk",
+      PlanProtocol: "v1",
       PlanGcsUri: "gs://b/renders/r1/plan.tar.gz",
       PlanHash: PLAN_HASH,
       ChunkIndex: 2,
@@ -220,6 +222,7 @@ describe("dispatch", () => {
     await seedPlanTar(gcs, "gs://b/renders/r1/plan.tar.gz", PLAN_HASH);
     const event: RenderChunkEvent = {
       Action: "renderChunk",
+      PlanProtocol: "v1",
       PlanGcsUri: "gs://b/renders/r1/plan.tar.gz",
       PlanHash: "WRONG_HASH",
       ChunkIndex: 0,
@@ -236,6 +239,7 @@ describe("dispatch", () => {
     gcs.seed("gs://b/renders/r1/chunks/0001.mp4", Buffer.from("c1"));
     const event: AssembleEvent = {
       Action: "assemble",
+      PlanProtocol: "v1",
       PlanGcsUri: "gs://b/renders/r1/plan.tar.gz",
       ChunkGcsUris: ["gs://b/renders/r1/chunks/0000.mp4", "gs://b/renders/r1/chunks/0001.mp4"],
       AudioGcsUri: null,
@@ -251,7 +255,7 @@ describe("dispatch", () => {
   // This end-to-end adapter contract is intentionally one narrative test: it
   // verifies ordering and target isolation across all three handler roles.
   // fallow-ignore-next-line complexity
-  it("runs v2 plan → target-scoped chunk → assemble with manifest-last CAS", async () => {
+  it("defaults omitted plan protocol to v2 across plan → chunk → assemble", async () => {
     const gcs = new FakeGcs();
     await seedProjectTar(gcs, "gs://b/sites/v2/project.tar.gz");
     const root = mkTmp("hf-v2-e2e-");
@@ -306,7 +310,6 @@ describe("dispatch", () => {
     const planned = await dispatch(
       {
         Action: "plan",
-        PlanProtocol: "v2",
         ProjectGcsUri: "gs://b/sites/v2/project.tar.gz",
         PlanOutputGcsPrefix: "gs://b/renders/v2/",
         Config: { fps: 30, width: 640, height: 360, format: "mp4" },
@@ -326,7 +329,6 @@ describe("dispatch", () => {
     await dispatch(
       {
         Action: "plan",
-        PlanProtocol: "v2",
         ProjectGcsUri: "gs://b/sites/v2/project.tar.gz",
         PlanOutputGcsPrefix: "gs://b/renders/v2/",
         Config: { fps: 30, width: 640, height: 360, format: "mp4" },
@@ -342,7 +344,6 @@ describe("dispatch", () => {
     const chunk = await dispatch(
       {
         Action: "renderChunk",
-        PlanProtocol: "v2",
         PlanV2ManifestGcsUri: planned.PlanV2ManifestGcsUri,
         PlanV2ArtifactGcsPrefix: planned.PlanV2ArtifactGcsPrefix,
         PlanHash: planned.PlanHash,
@@ -360,7 +361,6 @@ describe("dispatch", () => {
     await dispatch(
       {
         Action: "assemble",
-        PlanProtocol: "v2",
         PlanV2ManifestGcsUri: planned.PlanV2ManifestGcsUri,
         PlanV2ArtifactGcsPrefix: planned.PlanV2ArtifactGcsPrefix,
         PlanHash: planned.PlanHash,
@@ -409,6 +409,7 @@ describe("bucket allowlist guard", () => {
     try {
       const event: RenderChunkEvent = {
         Action: "renderChunk",
+        PlanProtocol: "v1",
         PlanGcsUri: "gs://evil-bucket/plan.tar.gz",
         PlanHash: PLAN_HASH,
         ChunkIndex: 0,
@@ -451,6 +452,7 @@ describe("bucket allowlist guard", () => {
     try {
       const event: RenderChunkEvent = {
         Action: "renderChunk",
+        PlanProtocol: "v1",
         PlanGcsUri: "gs://any-bucket/renders/r1/plan.tar.gz",
         PlanHash: PLAN_HASH,
         ChunkIndex: 0,
@@ -476,6 +478,7 @@ describe("createApp HTTP mapping", () => {
       headers: { "content-type": "application/json" },
       body: JSON.stringify({
         Action: "renderChunk",
+        PlanProtocol: "v1",
         PlanGcsUri: "gs://b/renders/r1/plan.tar.gz",
         PlanHash: PLAN_HASH,
         ChunkIndex: 0,
@@ -497,6 +500,7 @@ describe("createApp HTTP mapping", () => {
       headers: { "content-type": "application/json" },
       body: JSON.stringify({
         Action: "renderChunk",
+        PlanProtocol: "v1",
         PlanGcsUri: "gs://b/renders/r1/plan.tar.gz",
         PlanHash: "WRONG",
         ChunkIndex: 0,
@@ -524,6 +528,7 @@ describe("createApp HTTP mapping", () => {
       headers: { "content-type": "application/json" },
       body: JSON.stringify({
         Action: "renderChunk",
+        PlanProtocol: "v1",
         PlanGcsUri: "gs://b/renders/r1/plan.tar.gz",
         PlanHash: PLAN_HASH,
         ChunkIndex: 0,
@@ -561,6 +566,7 @@ describe("createApp HTTP mapping", () => {
         headers: { "content-type": "application/json" },
         body: JSON.stringify({
           Action: "renderChunk",
+          PlanProtocol: "v1",
           PlanGcsUri: "gs://b/renders/r1/plan.tar.gz",
           PlanHash: PLAN_HASH,
           ChunkIndex: 0,
@@ -598,6 +604,7 @@ describe("createApp HTTP mapping", () => {
       headers: { "content-type": "application/json" },
       body: JSON.stringify({
         Action: "renderChunk",
+        PlanProtocol: "v1",
         PlanGcsUri: "gs://b/renders/r1/plan.tar.gz",
         PlanHash: PLAN_HASH,
         ChunkIndex: 0,
@@ -626,6 +633,7 @@ describe("createApp HTTP mapping", () => {
       headers: { "content-type": "application/json" },
       body: JSON.stringify({
         Action: "plan",
+        PlanProtocol: "v1",
         ProjectGcsUri: "gs://b/sites/invalid-video-metadata/project.tar.gz",
         PlanOutputGcsPrefix: "gs://b/renders/invalid-video-metadata/",
         Config: { fps: 30, width: 640, height: 360, format: "mp4" },
@@ -645,6 +653,7 @@ describe("createApp HTTP mapping", () => {
       headers: { "content-type": "application/json" },
       body: JSON.stringify({
         Action: "renderChunk",
+        PlanProtocol: "v1",
         PlanGcsUri: "gs://b/renders/r1/missing.tar.gz",
         PlanHash: PLAN_HASH,
         ChunkIndex: 0,
diff --git a/packages/gcp-cloud-run/src/server.ts b/packages/gcp-cloud-run/src/server.ts
index 81aae4c2b..8d467ec7a 100644
--- a/packages/gcp-cloud-run/src/server.ts
+++ b/packages/gcp-cloud-run/src/server.ts
@@ -46,13 +46,16 @@ import {
 import { resolveChromeExecutablePath } from "./chromium.js";
 import type {
   AssembleEvent,
+  AssembleV2Event,
   AssembleResultBody,
   CloudRunAction,
   CloudRunEvent,
   CloudRunResult,
   PlanEvent,
+  PlanV2Event,
   PlanResultBody,
   RenderChunkEvent,
+  RenderChunkV2Event,
   RenderChunkResultBody,
 } from "./events.js";
 import { type DistributedFormat, formatExtension } from "./formatExtension.js";
@@ -155,21 +158,22 @@ function validatePlanProtocolShape(event: PlanEvent | RenderChunkEvent | Assembl
   }
   if (event.Action === "plan") return;
 
+  const effectiveProtocol = protocol ?? "v2";
   const hasV1Locator = typeof raw.PlanGcsUri === "string";
   const hasV2Manifest = typeof raw.PlanV2ManifestGcsUri === "string";
   const hasV2Prefix = typeof raw.PlanV2ArtifactGcsPrefix === "string";
   const valid =
-    protocol === "v2"
+    effectiveProtocol === "v2"
       ? !hasV1Locator && hasV2Manifest && hasV2Prefix
       : hasV1Locator && !hasV2Manifest && !hasV2Prefix;
   if (!valid) {
     const error = new Error(
-      `[handler] ${protocol === "v2" ? "v2" : "v1"} ${event.Action} event has mixed or missing plan locators`,
+      `[handler] ${effectiveProtocol} ${event.Action} event has mixed or missing plan locators`,
     );
     error.name = "PLAN_PROTOCOL_UNSUPPORTED";
     throw error;
   }
-  if (protocol === "v2" && event.Action === "assemble" && event.AudioGcsUri !== null) {
+  if (effectiveProtocol === "v2" && event.Action === "assemble" && event.AudioGcsUri !== null) {
     const error = new Error("[handler] v2 assemble audio must be materialized from the manifest");
     error.name = "PLAN_PROTOCOL_UNSUPPORTED";
     throw error;
@@ -254,14 +258,14 @@ function summarizeEvent(
       return {
         projectGcsUri: event.ProjectGcsUri,
         planOutputGcsPrefix: event.PlanOutputGcsPrefix,
-        planProtocol: event.PlanProtocol ?? "v1",
+        planProtocol: event.PlanProtocol ?? "v2",
         format: event.Config.format,
         fps: event.Config.fps,
       };
     case "renderChunk":
       return {
-        planProtocol: event.PlanProtocol ?? "v1",
-        ...(event.PlanProtocol === "v2"
+        planProtocol: event.PlanProtocol ?? "v2",
+        ...(event.PlanProtocol !== "v1"
           ? { planV2ManifestGcsUri: event.PlanV2ManifestGcsUri }
           : { planGcsUri: event.PlanGcsUri }),
         chunkIndex: event.ChunkIndex,
@@ -269,8 +273,8 @@ function summarizeEvent(
       };
     case "assemble":
       return {
-        planProtocol: event.PlanProtocol ?? "v1",
-        ...(event.PlanProtocol === "v2"
+        planProtocol: event.PlanProtocol ?? "v2",
+        ...(event.PlanProtocol !== "v1"
           ? { planV2ManifestGcsUri: event.PlanV2ManifestGcsUri }
           : { planGcsUri: event.PlanGcsUri }),
         chunkCount: event.ChunkGcsUris.length,
@@ -297,7 +301,7 @@ function primeChrome(deps?: HandlerDeps): void {
 
 // fallow-ignore-next-line complexity
 async function handlePlan(event: PlanEvent, deps?: HandlerDeps): Promise<PlanResultBody> {
-  if (event.PlanProtocol === "v2") {
+  if (event.PlanProtocol !== "v1") {
     return handlePlanV2(event, deps);
   }
   const started = Date.now();
@@ -365,7 +369,7 @@ async function handlePlan(event: PlanEvent, deps?: HandlerDeps): Promise<PlanRes
  */
 // fallow-ignore-next-line complexity
 async function handlePlanV2(
-  event: Extract<PlanEvent, { PlanProtocol: "v2" }>,
+  event: PlanV2Event,
   deps?: HandlerDeps,
 ): Promise<Extract<PlanResultBody, { PlanProtocol: "v2" }>> {
   const started = Date.now();
@@ -418,7 +422,7 @@ async function handleRenderChunk(
   event: RenderChunkEvent,
   deps?: HandlerDeps,
 ): Promise<RenderChunkResultBody> {
-  if (event.PlanProtocol === "v2") {
+  if (event.PlanProtocol !== "v1") {
     return handleRenderChunkV2(event, deps);
   }
   const started = Date.now();
@@ -475,7 +479,7 @@ async function handleRenderChunk(
 /** Materialize only this chunk's verified v2 dependencies before rendering. */
 // fallow-ignore-next-line complexity
 async function handleRenderChunkV2(
-  event: Extract<RenderChunkEvent, { PlanProtocol: "v2" }>,
+  event: RenderChunkV2Event,
   deps?: HandlerDeps,
 ): Promise<RenderChunkResultBody> {
   const started = Date.now();
@@ -548,7 +552,7 @@ async function handleAssemble(
   event: AssembleEvent,
   deps?: HandlerDeps,
 ): Promise<AssembleResultBody> {
-  if (event.PlanProtocol === "v2") {
+  if (event.PlanProtocol !== "v1") {
     return handleAssembleV2(event, deps);
   }
   const started = Date.now();
@@ -613,7 +617,7 @@ async function handleAssemble(
  */
 // fallow-ignore-next-line complexity
 async function handleAssembleV2(
-  event: Extract<AssembleEvent, { PlanProtocol: "v2" }>,
+  event: AssembleV2Event,
   deps?: HandlerDeps,
 ): Promise<AssembleResultBody> {
   const started = Date.now();
@@ -781,12 +785,12 @@ function getEventGcsUris(event: PlanEvent | RenderChunkEvent | AssembleEvent): s
     case "plan":
       return [event.ProjectGcsUri, event.PlanOutputGcsPrefix];
     case "renderChunk":
-      return event.PlanProtocol === "v2"
+      return event.PlanProtocol !== "v1"
         ? [event.PlanV2ManifestGcsUri, event.PlanV2ArtifactGcsPrefix, event.ChunkOutputGcsPrefix]
         : [event.PlanGcsUri, event.ChunkOutputGcsPrefix];
     case "assemble":
       return [
-        ...(event.PlanProtocol === "v2"
+        ...(event.PlanProtocol !== "v1"
           ? [event.PlanV2ManifestGcsUri, event.PlanV2ArtifactGcsPrefix]
           : [event.PlanGcsUri]),
         ...event.ChunkGcsUris,
diff --git a/packages/gcp-cloud-run/terraform/smoke-safety.test.ts b/packages/gcp-cloud-run/terraform/smoke-safety.test.ts
index 4ba0df321..faaa03b1d 100644
--- a/packages/gcp-cloud-run/terraform/smoke-safety.test.ts
+++ b/packages/gcp-cloud-run/terraform/smoke-safety.test.ts
@@ -7,8 +7,8 @@ const smoke = readFileSync(smokePath, "utf-8");
 const dockerfile = readFileSync(join(import.meta.dir, "../Dockerfile"), "utf-8");
 
 describe("GCP smoke ownership and protocol safety", () => {
-  it("defaults to v1 and requires an explicit v2 protocol argument", () => {
-    expect(smoke).toContain('PROTOCOLS="${PROTOCOLS:-v1}"');
+  it("defaults to v2 and retains explicit v1/v2 protocol arguments", () => {
+    expect(smoke).toContain('PROTOCOLS="${PROTOCOLS:-v2}"');
     expect(smoke).toContain("--protocols)");
     expect(smoke).toContain("PlanProtocol: $protocol");
     expect(smoke).toContain("decodedFramesEqual");
diff --git a/packages/gcp-cloud-run/terraform/workflow.test.ts b/packages/gcp-cloud-run/terraform/workflow.test.ts
index b17e00772..e4c9f5d92 100644
--- a/packages/gcp-cloud-run/terraform/workflow.test.ts
+++ b/packages/gcp-cloud-run/terraform/workflow.test.ts
@@ -77,8 +77,8 @@ describe("Cloud Workflows plan protocol routing", () => {
     expect(source.match(/max_retries: 4/g)).toHaveLength(4);
   });
 
-  it("keeps v1 as the default and rejects unknown protocols before plan", () => {
-    expect(source).toContain('default(map.get(args, "PlanProtocol"), "v1")');
+  it("defaults omitted protocol to v2 and rejects unknown protocols before plan", () => {
+    expect(source).toContain('default(map.get(args, "PlanProtocol"), "v2")');
     expect(namedStep("selectPlanProtocol")).toMatchObject({
       next: "unsupportedPlanProtocol",
     });
diff --git a/packages/gcp-cloud-run/terraform/workflow.yaml b/packages/gcp-cloud-run/terraform/workflow.yaml
index 7901a5a2b..2e563a489 100644
--- a/packages/gcp-cloud-run/terraform/workflow.yaml
+++ b/packages/gcp-cloud-run/terraform/workflow.yaml
@@ -26,9 +26,9 @@ main:
           - planOutputGcsPrefix: ${args.PlanOutputGcsPrefix}
           - outputGcsUri: ${args.OutputGcsUri}
           - config: ${args.Config}
-          # Backward-compatible default. v2 is accepted only through an
-          # explicit top-level PlanProtocol opt-in.
-          - planProtocol: ${default(map.get(args, "PlanProtocol"), "v1")}
+          # Plan v2 is the default. Explicit v1 remains available during the
+          # deprecated monolithic-plan compatibility window.
+          - planProtocol: ${default(map.get(args, "PlanProtocol"), "v2")}
 
     # ── Plan (Activity A) ────────────────────────────────────────────────────
     - selectPlanProtocol: