Function guide

Best AI models for function calling

This page is built for teams that need models to call tools reliably, return machine-friendly payloads, and keep enough context for multi-step orchestration.

Live signalTool support for function and action calls

Live signalStructured output support for predictable payloads

Live signalEnough context for orchestration prompts and state

Live signalLive pricing for automation-heavy production use

Fast answer

Start with the live shortlist, then validate the route

Function calling is a core building block for agents, but this page is more narrowly focused on tool orchestration and reliable machine-to-machine output.

Data source and freshness

Catalog-backed, not a static price sheet

TVP refreshes this page from the live OpenRouter model catalog. This render used 428 public model records and was synchronized Jul 14, 2026, 9:32 PM UTC. Pricing, availability, and context values can change.

Verify the exact route before sending production traffic, then use the linked model and provider pages as the source for current values. Read the TVP data methodology.

Shortlist

Top live candidates right now

meta-llama

Meta: Llama 4 Scout

Llama 4 Scout 17B Instruct (16E) is a mixture-of-experts (MoE) language model developed by Meta, activating 17 billion parameters out of a total of 109B. It supports native multimodal input...

Context10,000,000

Input$0.1

Output$0.3

10,000,000 token context, tool support, and structured output make it suitable for orchestration-heavy workflows.

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tools
structured

Model details Provider page

x-ai

xAI: Grok 4.20

Grok 4.20 is a reasoning model from xAI with industry-leading speed and agentic tool calling capabilities. It combines the lowest hallucination rate on the market with strict prompt adherance, delivering...

Context2,000,000

Input$1.25

Output$2.50

2,000,000 token context, tool support, and structured output make it suitable for orchestration-heavy workflows.

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image
file
tools
structured

Model details Provider page

openai

OpenAI: GPT-5.6 Luna

GPT-5.6 Luna is a fast, cost-efficient model in OpenAI's GPT-5.6 series. It is suited for high-volume, latency-sensitive tasks such as chat, classification, and lightweight agentic workflows, providing capable reasoning for...

Context1,050,000

Input$1.00

Output$6.00

1,050,000 token context, tool support, and structured output make it suitable for orchestration-heavy workflows.

file
image
text
tools
structured

Model details Provider page

openai

OpenAI: GPT-5.6 Luna Pro

GPT-5.6 Luna Pro is the same underlying model as [GPT-5.6 Luna](TVP catalog), served with `reasoning.mode` set to `pro` for higher-quality responses on complex tasks. Learn more in OpenAI's docs: https://developers.openai.com/api/docs/guides/reasoning#reasoning-mode

Context1,050,000

Input$1.00

Output$6.00

1,050,000 token context, tool support, and structured output make it suitable for orchestration-heavy workflows.

file
image
text
tools
structured

Model details Provider page

openai

OpenAI: GPT-5.4

GPT-5.4 is OpenAI’s latest frontier model, unifying the Codex and GPT lines into a single system. It features a 1M+ token context window (922K input, 128K output) with support for...

Context1,050,000

Input$2.50

Output$15.00

1,050,000 token context, tool support, and structured output make it suitable for orchestration-heavy workflows.

text
image
file
tools
structured

Model details Provider page

FAQ

What buyers usually ask

Is function calling the same as agents?

Function calling is a core building block for agents, but this page is more narrowly focused on tool orchestration and reliable machine-to-machine output.

Why compare structured output here?

Because orchestration breaks down when outputs are inconsistent. Models that support structured formats are easier to plug into production systems.

Next step

Use the guide, then validate the route in live TVP data.

TVP keeps the shortlist connected to the current catalog, provider coverage, and token pricing so buyers can move from research to routing without starting over.

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