Incorrect cost calculation for generic OpenAI-compatible providers (Zenmux) using prefixed model IDs

Description

Environment

• Opencode Version: 1.8.18
• OS: Linux
• Provider: Zenmux (configured via opencode connect as OpenAI-compatible)
• Model used: deepseek/deepseek-v4-flash

Summary

When using generic OpenAI-compatible proxy providers like Zenmux, session cost calculation in the TUI is inaccurate. While OpenRouter correctly reports total costs, generic providers using prefixed model IDs (vendor/model-name) seem to default input token costs to $0.00, displaying only the output token cost.

Root Cause / Hypothesis

OpenRouter has native integration/pricing retrieval in Opencode. However, for generic OpenAI-compatible endpoints, Opencode falls back to a local model pricing lookup. The vendor prefix (e.g., deepseek/ in deepseek/deepseek-v4-flash) prevents matching the model in the internal pricing table, causing input cost calculation to default to 0.

Proof

In a session with 57 API calls using deepseek/deepseek-v4-flash via Zenmux:

• Zenmux Dashboard:
  • Input Cost: $0.1533 (2.28M tokens)
  • Output Cost: $0.0410 (32.60K tokens)
  • Total Cost: $0.1944
• Opencode TUI:
  • Displayed Cost: $0.04

The $0.04 figure corresponds strictly to the Output Cost, completely ignoring the Input Cost.

Expected Behavior

Opencode should either:

1. Strip vendor prefixes when doing local pricing lookups for generic OpenAI-compatible providers.
2. Allow fallback/custom token pricing definitions in configuration for non-standard providers.

Actual Behavior

Input costs are calculated as $0 when the model string contains a vendor prefix on generic OpenAI-compatible endpoints.

Plugins

none

OpenCode version

1.8.18

Steps to reproduce

1. Connect a generic OpenAI-compatible aggregator provider (Zenmux.ai) using opencode connect.
2. Select a model using a vendor prefix in its ID (e.g., deepseek/deepseek-v4-flash).
3. Run a session generating both input and output usage across multiple requests.
4. Compare the session cost shown in the OpenCode TUI with the actual costs logged on the provider dashboard.

Observed: The OpenCode TUI displays $0.04, which strictly equals the output token cost ($0.0410). The input token cost ($0.1533) is completely ignored/calculated as $0.
Expected: Total session cost should sum both input and output token costs ($0.1944).

Screenshot and/or share link

Comparison from a 57-request session:

• Zenmux Dashboard: Input $0.1533 (2.28M tokens) | Output $0.0410 (32.60K tokens) | Total $0.1944
• OpenCode TUI: Displays $0.04 (matches Output Cost only)

Operating System

Linux / Ubuntu 24.04.04 LTS

Terminal

Xfce Terminal with bash