Copilot stopped work due to an error Execution failed: Error: Model "claude-sonnet-4.6" is not available.

[MatthewMalcolm]

🏷️ Discussion Type

Bug

💬 Feature/Topic Area

ARC (Actions Runner Controller)

Discussion Details

this morning I am unable to talk to Cop[ilot Chat. Every Agent has the same error. I manually told it to Use Opus 4.8 instead and still it tries to contact sonnet 4.6 and fails. How do we stop this issue from happening. ?
Snippet from Agent . Shows it finds 4.8 then tries 4.6 even though I told it to not use it and it is not visibale in the allow list today

Resolved base commit 'main' to SHA: f9d59692cdeabc21003183851c3a4fbed15a768c (via FETCH_HEAD)
Fetching CodeQL release info without authentication (may hit rate limits)
CodeQL asset ID: 523665808
CodeQL downloaded to /tmp/codeql-scratch-88e623166e27dcb0/codeql-download/codeql-bundle-linux64.tar.gz
CodeQL unzipped to /tmp/codeql-scratch-88e623166e27dcb0
[memory] expAssignmentContextSource present: true
Memory enablement check: enabled
[cca-engine] Model resolution: env="sweagent-capi:claude-opus-4.8" settings="sweagent-capi:claude-opus-4.8" → resolved="claude-opus-4.8"
[cca-engine] Reasoning effort resolution: env="" settings="(not set)" → resolved="medium"
[cca-engine] CopilotClient log level set to "info" (COPILOT_AGENT_DEBUG=false)
[cca-engine] CLI path not set; SDK will resolve @github/copilot bundled CLI
[cca-engine] Discovering MCP tools from proxy...
[cca-engine] Discovered MCP server: github-mcp-server
[cca-engine] Discovered MCP server: playwright
[cca-engine] fetchProgress returned 1 raw record(s).
[cca-engine] Parsed 1 session-events record(s): 1 v3, 0 manifest(s), 0 chunk(s); 1 candidate snapshot(s).
[cca-engine] Restored session state for 035e4dbe-7a55-4953-b550-8f932b2e22de (404617 bytes, single record).
[cca-engine] MCP permission gate disabled — all tool calls auto-approved
[cca-engine] CCA V3 CAPI proxy listening on http://127.0.0.1:35683,/ forwarding to https://api.individual.githubcopilot.com/
[cca-engine] Routing host-provided ExP assignment context into the SDK session for telemetry attribution (flights carried through: [none])
[cca-engine] Attempting to resume session 035e4dbe-7a55-4953-b550-8f932b2e22de (behavior=seed-history)...
[cca-engine] Session 035e4dbe-7a55-4953-b550-8f932b2e22de (resumed=true)
[cca-engine] Steering mode: mission-control session=731eaa72-852d-4ed6-b521-abb0105a4af1 callback_accepts_user_messages=false
[cca-engine] Sending prompt for action=task...
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'github-mcp-server': pending
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'playwright': pending
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'engine-tools': pending
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'runtime-tools': pending
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'engine-tools': connected
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'playwright': connected
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'github-mcp-server': connected
[cca-engine] in-session runtime checkQuota callback v3: preRequest invoked (turn=0)
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'runtime-tools': connected
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'runtime-tools': connected
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'github-mcp-server': connected
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'playwright': connected
[cca-engine] [session=035e4dbe-7a55-4953-b550-8f932b2e22de] MCP server 'engine-tools': connected
[cca-engine] turn=0 session.error: Execution failed: Error: Model "claude-sonnet-4.6" is not available.
[cca-engine] turn=0 session.idle
[cca-engine] in-session runtime checkQuota callback v3: quota is sufficient, continuing session (turn=0)
[cca-engine] Error: Error: Execution failed: Error: Model "claude-sonnet-4.6" is not available.
[cca-engine] Committing and pushing any changes that occurred before error
[cca-engine] CCA V3 CAPI proxy stopped
[cca-engine] Fatal: Error: Execution failed: Error: Model "claude-sonnet-4.6" is not available.
Stack trace: Error: Model "claude-sonnet-4.6" is not available.
at LS.resolveAndValidateModel (file:///home/runner/_work/_temp/-action-main/dist-cca-v3/node_modules/@github/copilot-linux-x64/app.js:2419:10010)
[FALLBACK ERROR] Copilot has encountered an unexpected error: [runtime:unclassified] Execution failed: Error: Model "claude-sonnet-4.6" is not available.
[cca-engine] Emitted fallback error annotation for fatal error
at async LS.buildSettingsAndTools (file:///home/runner/_work/_temp/-action-main/dist-cca-v3/node_modules/@github/copilot-linux-x64/app.js:2417:58328)
forceExit is shutting down the process
at async LS.runAgenticLoop (file:///home/runner/_work/_temp/-action-main/dist-cca-v3/node_modules/@github/copilot-linux-x64/app.js:2419:29007)
at async LS.runNativeMessageTurn (file:///home/runner/_work/_temp/-action-main/dist-cca-v3/node_modules/@github/copilot-linux-x64/app.js:2417:27307)
at async LS.invokeNativeSessionHostEffect (file:///home/runner/_work/_temp/-action-main/dist-cca-v3/node_modules/@github/copilot-linux-x64/app.js:2398:147020)
at async LS.handleNativeSessionBridgeCall (file:///home/runner/_work/_temp/-action-main/dist-cca-v3/node_modules/@github/copilot-linux-x64/app.js:2398:145620)
Stopping git-proxy (pid=256)...
::***::
Error: Copilot has encountered an unexpected error: [runtime:unclassified] Execution failed: Error: Model "claude-sonnet-4.6" is not available.
Error: Process completed with exit code 1.

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[MatthewMalcolm]

I found that the 4.6 was retired two days ago and for what every reason the work I was doing last night has decided to resume on 4.6 and this is apparently not fixable. So throw away the wasted credits and start again apparently and it should stop trying to use the model that has not exists for two days
No idea why or how this decided to do that,. I hope this helps someone else