Head-to-head comparison
Phi 3.5 mini instruct (Microsoft) and Phi 4 reasoning plus (Microsoft) compared on the ModelCap Index, API price, context window, provider availability, weight access and every public benchmark board they share. Figures are the same ones shown on the live rankings; nothing here is a hidden score.
Snapshot as of 22 September 2026
As of 22 September 2026, Phi 3.5 mini instruct holds the stronger ModelCap Index position (#185 vs #220).
Evidence: global-corpus-prior over 208 held-out anchors (26%); launch card against 4 resolved peers on 6 rows (74%); exceeds every named peer on 1 of 6 rows; optimism haircut 0.67 from cross-lab-probe; shrunk 11.5 up toward the measured corpus · finetune of microsoft/phi-4 · finetune (100%). Prices are the lowest listed API offer per million tokens observed on the OpenRouter catalogue.
Neither model has a published result on a public benchmark board ModelCap tracks yet.
Scores are the sources' own published figures for each model's best evaluated configuration; ModelCap never re-runs a benchmark.
Want a different pairing? Open the interactive comparison tool to swap either model for any current ranked language model.
Phi 3.5 mini instruct ranks higher on the ModelCap Index as of 22 September 2026: #185 against #220. That is a capability ranking built from public benchmark evidence with published uncertainty; whether it is "better" for you also depends on price, context and where you can run it. Their published uncertainty intervals overlap, so the rank difference alone does not establish a reliable capability advantage for your workload.
At least one of the two has no listed API price on ModelCap right now, so no price comparison is made.
Both publish a —-token context window.
The two models do not share a coding benchmark board on ModelCap yet, so no head-to-head coding score is published; the ModelCap Index position is the closest overall signal.
Phi 3.5 mini instruct: Open weights. Phi 4 reasoning plus: Open weights. Open weights mean the checkpoint can be downloaded and self-hosted under its licence; API-only models are available solely through hosted endpoints.
ModelCap currently lists 0 API providers for Phi 3.5 mini instruct and 0 for Phi 4 reasoning plus, from the OpenRouter catalogue snapshot the site serves; each model page lists the providers and their prices.
Every figure comes from the sealed ModelCap dataset published 22 September 2026; the page re-renders within a minute of each data refresh, and the ModelCap Index positions are the same ones shown on the live rankings.