OpenCode immediately triggers “Input exceeds context window” and auto-compaction in empty sessions after latest update #27315

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1. github-actions

   assigned

   kitlangton

   on May 13, 2026
2. github-actions commented on May 13, 2026

   

   github-actionsBot

   on May 13, 2026 – with GitHub Actions

   Contributor

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   This issue might be a duplicate of existing issues. Please check:

   • Instant compaction on first github-copilot/gpt-5.4 prompt with 3 screenshots #19863: Instant compaction on first prompt with GPT-5.x model in a fresh session (similar symptom: immediate compaction before any meaningful conversation history)
   • Large AGENTS.md files consume entire context window, triggering immediate compaction #18037: Immediate compaction triggered on first turn (different cause — large AGENTS.md — but same "compaction on first message" symptom that may share root cause)
3. evscott commented on May 13, 2026

   

   evscott

   on May 13, 2026

   Last edited by evscott

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   I think I narrowed this down to having something to do with the Posthog MCP. Removing it from my config resolves the issue.

   For example, this is my config which results in Input exceeds context window of the model

   {
     "$schema": "https://opencode.ai/config.json",
     "mcp": {
       "posthog": {
         "type": "remote",
         "url": "https://mcp.posthog.com/mcp",
         "enabled": true
       },
       "sentry": {
         "type": "remote",
         "url": "https://mcp.sentry.dev/mcp",
         "oauth": {},
         "enabled": true
       },
     },
     "agent": {
       "plan": {
         "model": "openai/gpt-5.5",
         "tools": {
           "write": false,
           "edit": false,
           "bash": true,
           "webfetch": true
         }
       },
       "build": {
         "model": "openai/gpt-5.5",
         "tools": {
           "write": true,
           "edit": true,
           "bash": true,
           "webfetch": true
         }
       },
     }
   }
   

   Whereas this works fine

   {
     "$schema": "https://opencode.ai/config.json",
     "mcp": {
       "sentry": {
         "type": "remote",
         "url": "https://mcp.sentry.dev/mcp",
         "oauth": {},
         "enabled": true
       },
     },
     "agent": {
       "plan": {
         "model": "openai/gpt-5.5",
         "tools": {
           "write": false,
           "edit": false,
           "bash": true,
           "webfetch": true
         }
       },
       "build": {
         "model": "openai/gpt-5.5",
         "tools": {
           "write": true,
           "edit": true,
           "bash": true,
           "webfetch": true
         }
       },
     }
   }
   

   I'll leave open the issue incase you want to do something about this (not sure what). But, feel free to close it otherwise. I'm unblocked at least.
4. antonlvovych commented on May 13, 2026

   

   antonlvovych

   on May 13, 2026

   Last edited by antonlvovych

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   same for me - also just after installed posthog mcp. endless auto compaction loop starting with any session, including completely new ones
5. rekram1-node

   closed this as not plannedon Jun 12, 2026
6. rekram1-node

   closed this as a duplicateof [FEATURE]:Add mcp search tool, reduce mcp tool occupying a lot of context #8625 on Jun 12, 2026