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Custom "anthropic" provider does not enforce provider.max_prompt_tokens — sessions grow past the model context window until a hard 400

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#2,355 1 comentario 0 reacciones 0 asignados Ver en GitHub

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Evaluación

Dificultad
4/5
Tiempo estimado
3-5 días
Aptitud para principiantes
48/100
Tipo de issue
Error
Claridad
Bastante claro
Estado de actividad
Activo
Stack tecnológico
java
Área
api, backend

Línea de trabajo

Comienza en la ruta session-create/resume del proveedor anthropic personalizado y rastrea cómo se gestionan max_prompt_tokens y los umbrales de infinite_sessions antes de enviar las solicitudes. Compara esa ruta con la ruta del backend de Copilot, donde funciona la compactación, reproduce la transcripción creciente y confirma que los prompts se mantienen dentro del presupuesto configurado y que las sesiones fallidas pueden recuperarse.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

bug

Summary

When a custom provider of type: "anthropic" is configured with max_prompt_tokens, the SDK does not appear to enforce that budget. A long-running session keeps accumulating transcript until the request exceeds the model's context window and the provider rejects it with HTTP 400 -- after which the session is permanently unusable.

Configuration

The provider is created on every session create/resume with an explicit prompt budget:

{
  "type": "anthropic",
  "base_url": "...",
  "model_id": "claude-sonnet-5",
  "max_output_tokens": 32768,
  "max_prompt_tokens": 967232
}

max_prompt_tokens is derived as context_window (1,000,000) - max_output_tokens (32,768) = 967,232.

Expected

The SDK compacts (or otherwise bounds the prompt) before crossing max_prompt_tokens = 967232.

Actual

The transcript grew unbounded to 1,001,142 tokens -- 33,910 past the configured budget, and past the model's 1,000,000 hard limit:

400 invalid_request_error
"prompt is too long: 1001142 tokens > 1000000 maximum"

The session had run ~18 successful turns over ~3 hours, with the serialized request growing steadily (~1.98 MB -> ~2.04 MB) before crossing the limit. Tool count was constant throughout, so the growth is accumulated conversation history rather than tool schemas.

Two additional observations

  1. infinite_sessions thresholds also appear inert on this path. background_compaction_threshold / buffer_exhaustion_threshold are sent on every turn but appear to have no effect for the anthropic provider (they do take effect on the Copilot backend path). So neither the threshold-based compaction nor the max_prompt_tokens budget bounded the transcript.

  2. The session actively degrades after the first failure. Once over the limit, continued turns keep appending to the transcript -- request size grew from ~2.044 MB to ~2.065 MB across ~30 consecutive failed turns. There is no back-off, trim, or compaction triggered by the 400, so the session can never self-recover; every subsequent turn fails immediately (~1.5s vs. the 38s first failure).

Impact

Every turn in an affected session fails permanently. The only recovery is to start a new session, and nothing in the surfaced error indicates that to the user. Because the failure is a deterministic 400, retry suppression correctly kicks in -- but that just means the session is durably wedged.

Environment

  • SDK 1.0.7 / Copilot CLI 1.0.71
  • Custom anthropic provider over an OpenAI-incompatible relay endpoint
  • Model claude-sonnet-5 (1,000,000-token context window)

Ask

Should provider.max_prompt_tokens be enforced on the anthropic provider path (and/or should infinite_sessions compaction apply there)? If enforcement is intentionally backend-only today, it would help to document that clearly, since the field is accepted without warning and silently has no effect.

Lenguaje dominante
TypeScript
Estrellas
10.5k
Forks
1.5k
Merge medio
1 d 7 h
PR fusionados (30 d)
98

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