Add MODELS.md with comprehensive list of available watsonx.ai models

MODELS.md

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+# Available watsonx.ai Models
+
+This document lists all foundation models currently available in watsonx.ai.
+
+## Chat & Text Generation Models
+
+| Model Label | Model ID | Provider | Parameters | Max Context |
+|------------|----------|----------|------------|-------------|
+| granite-3-8b-instruct | ibm/granite-3-8b-instruct | IBM | 8B | 8,192 |
+| granite-3.1-8b-instruct | ibm/granite-3.1-8b-instruct | IBM | 8B | 131,072 |
+| granite-4-h-small | ibm/granite-4-h-small | IBM | - | 131,072 |
+| llama-3-3-70b-instruct | meta-llama/llama-3-3-70b-instruct | Meta | 70B | 131,072 |
+| llama-guard-3-11b-vision | meta-llama/llama-guard-3-11b-vision | Meta | 11B | 131,072 |
+| mistral-large-2512 | mistral-large-2512 | Mistral AI | 675B (41B active) | - |
+| mistral-medium-2505 | mistralai/mistral-medium-2505 | Mistral AI | - | 131,072 |
+| mistral-small-3-1-24b-instruct-2503 | mistralai/mistral-small-3-1-24b-instruct-2503 | Mistral AI | 24B | 128,000 |
+| gpt-oss-120b | openai/gpt-oss-120b | OpenAI | 120B (5.1B active) | 131,072 |
+
+## Embedding Models
+
+| Model Label | Model ID | Provider | Dimensions | Max Tokens |
+|------------|----------|----------|------------|------------|
+| all-minilm6-v2 | sentence-transformers/all-minilm-l6-v2 | sentence-transformers | 384 | 512 |
+| slate-125m-english-rtrvr | ibm/slate-125m-english-rtrvr | IBM | - | - |
+| slate-30m-english-rtrvr | ibm/slate-30m-english-rtrvr | IBM | - | - |
+
+## Model Capabilities
+
+### IBM Granite Models
+- **granite-3-8b-instruct**: General-purpose instruction-following model
+- **granite-3.1-8b-instruct**: Enhanced version with extended context (131K tokens)
+- **granite-4-h-small**: Latest Granite 4 model with advanced capabilities
+
+### Meta Llama Models
+- **llama-3-3-70b-instruct**: Large instruction-tuned model with 70B parameters
+- **llama-guard-3-11b-vision**: Multimodal model with vision capabilities
+
+### Mistral Models
+- **mistral-large-2512**: State-of-the-art MoE model with 675B total parameters
+- **mistral-medium-2505**: Multimodal model with vision and extended context
+- **mistral-small-3-1-24b-instruct-2503**: Efficient 24B parameter model with vision
+
+### OpenAI Models
+- **gpt-oss-120b**: Open-weight model optimized for reasoning and agentic tasks
+
+## Supported Tasks
+
+All chat models support:
+- Question Answering
+- Summarization
+- Retrieval Augmented Generation (RAG)
+- Classification
+- Text Generation
+- Code Generation
+- Extraction
+- Translation
+- Function Calling
+
+## Usage Notes
+
+1. **Context Length**: Models with 131K+ context length support long-document processing
+2. **Vision Models**: Models with `image_chat` function support multimodal inputs
+3. **Function Calling**: Most models support OpenAI-compatible function calling
+4. **Multilingual**: Many models support multiple languages (see model specifications)
+
+## Model Selection Guide
+
+- **For general chat**: `ibm/granite-3-8b-instruct` or `meta-llama/llama-3-3-70b-instruct`
+- **For long context**: `ibm/granite-3.1-8b-instruct` or `mistralai/mistral-medium-2505`
+- **For vision tasks**: `meta-llama/llama-guard-3-11b-vision` or `mistralai/mistral-medium-2505`
+- **For embeddings**: `sentence-transformers/all-minilm-l6-v2` or `ibm/slate-125m-english-rtrvr`
+- **For reasoning**: `openai/gpt-oss-120b` or `mistral-large-2512`
+
+## API Version
+
+All models use API version: `2024-02-13`
+
+---
+
+*Last updated: 2026-02-23*
+*Source: watsonx.ai Foundation Model Specs API*