OpenAI: gpt-oss-20b (free)

GPT-OSS-20B (free) is a text-in, text-out model from OpenAI with a 131,072-token context window and a 32,768-token output ceiling. It supports tool use and reasoning, which means it can handle multi-step agentic workflows and function-calling tasks. Structured output support is unconfirmed, so developers who depend on guaranteed JSON schemas should verify behavior before building on it. The clearest reason to shortlist this model is cost: input and output are both priced at zero. That makes it a low-risk starting point for prototyping or low-budget projects where spending matters. The significant caveat is that there is no independent benchmark coverage yet, so its quality relative to other models in this price tier is genuinely unproven. Users who need verified performance data before committing should treat it as experimental until third-party evaluations are available.