feat: add context_tiers for arbitrary tiered pricing based on context length

[Pxys-io]

Problem

models.dev currently supports tiered pricing through cost.context_over_200k, which is hardcoded to a 200K token threshold. However, OpenRouter and other providers support tiered pricing at arbitrary context lengths (e.g., 200K, 500K, 1M), where each tier has different per-token rates.

This feature generalizes the tiered pricing system to match OpenRouter's tiered pricing format, where tiers are defined as an array with min_context thresholds.

Solution

New Schema: cost.context_tiers

An ordered array of pricing tiers, each with a min_context threshold. When the total input tokens (input + cache_read) meet or exceed a tier's threshold, that tier's pricing applies. Only the highest matching tier is used.

[cost]
input = 1.00
output = 3.00
cache_read = 0.20

# Tier 1: applies when input + cache_read >= 200,000 tokens
[[cost.context_tiers]]
min_context = 200_000
input = 2.00
output = 6.00
cache_read = 0.40

# Tier 2: applies when input + cache_read >= 500,000 tokens
[[cost.context_tiers]]
min_context = 500_000
input = 4.00
output = 12.00
cache_read = 0.80

Changes

File	Change
packages/core/src/schema.ts	Add ContextTier zod schema, context_tiers array field (max 4 tiers), validation that tiers are sorted by min_context ascending
providers/openrouter/models/xiaomi/mimo-v2-pro.toml	Example usage with 3-tier pricing (base, 200K, 500K)

Backward Compatibility

• context_over_200k is kept but marked as @deprecated
• Consumers should prefer context_tiers when present, falling back to context_over_200k for legacy models
• Existing models using context_over_200k continue to work unchanged

Consumer Changes (opencode)

A companion PR in opencode will:

1. Parse context_tiers from models.dev into the internal Model type
2. Replace the hardcoded 200_000 threshold in session/index.ts with dynamic tier selection
3. Fall back to experimentalOver200K for legacy models

[rekram1-node]

It's an interesting api, i was also considering something like:

cost_over: {
200_000: {...},
300_000: {....}
}

[Pxys-io]

It's an interesting api, i was also considering something like:

cost_over: {
200_000: {...},
300_000: {....}
}

Most I have seen is 128k and 256k etc, but I think flexible would be easier