[Bug] Anthropic API Error: Rate limit reached on claude-sonnet-4-6-1m with Claude Pro plan

Bug Description
I am on the Claude Pro plan and consistently receive API Error: Rate limit reached when using the claude-sonnet-4-6[1m] (1M context) model in Claude Code.
Steps to reproduce:

Open Claude Code with Pro plan
Run /model and select sonnet[1m] (claude-sonnet-4-6[1m])
Send any message (even "how are you")
Receive API Error: Rate limit reached

Expected behavior:
1M context model should be accessible on Pro plan, at least within reasonable usage limits.
Actual behavior:
Rate limit error is returned immediately and persistently. Issue has persisted for over 13 hours.
Additional context:

Default Sonnet 4.6 model works without any issues
Session usage is only 27% — well within limits
Extra usage budget: €0.74 / €50 spent (1%)
Waited 13+ hours — issue persists, ruling out temporary burst limiting
This suggests the 1M context model may be effectively inaccessible on Pro plan, which is not clearly documented

Environment:

Plan: Claude Pro
Claude Code version: 2.1.47
Model attempted: claude-sonnet-4-6[1m]
OS: macOS

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 2.1.50
• Feedback ID: bef02c6c-9d4d-4021-b1c6-d02ca73a5d64

Errors

[{"error":"RangeError [ERR_CHILD_PROCESS_STDIO_MAXBUFFER]: stdout maxBuffer length exceeded\n    at Socket.onChildStdout (node:child_process:484:14)\n    at Socket.emit (node:events:508:28)\n    at addChunk (node:internal/streams/readable:559:12)\n    at readableAddChunkPushByteMode (node:internal/streams/readable:510:3)\n    at Readable.push (node:internal/streams/readable:390:5)\n    at Pipe.onStreamRead (node:internal/stream_base_commons:189:23)","timestamp":"2026-02-22T07:38:38.864Z"},{"error":"Error: 429 {\"type\":\"error\",\"error\":{\"type\":\"rate_limit_error\",\"message\":\"Extra usage is required for long context requests.\"},\"request_id\":\"req_011CYNj7TmYSikEg9SLgfNhr\"}\n    at Z4.generate (file:///opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/cli.js:324:28283)\n    at QS.makeStatusError (file:///opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/cli.js:363:2195)\n    at QS.makeRequest (file:///opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/cli.js:363:5420)\n    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)","timestamp":"2026-02-22T07:38:54.949Z"},{"error":"Error: 429 {\"type\":\"error\",\"error\":{\"type\":\"rate_limit_error\",\"message\":\"Extra usage is required for long context requests.\"},\"request_id\":\"req_011CYNjFaXooocqrsFE9RGVH\"}\n    at Z4.generate (file:///opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/cli.js:324:28283)\n    at QS.makeStatusError (file:///opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/cli.js:363:2195)\n    at QS.makeRequest (file:///opt/homebrew/lib/node_modules/@anthropic-ai/claude-code/cli.js:363:5420)\n    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)","timestamp":"2026-02-22T07:40:45.135Z"}]