docs(readme): add GPT-5 mini/nano; usage note for reasoning effort; enums updated

Author: lucaromagnoli

README.md

@@ -132,6 +132,7 @@ auto response2 = client.sendRequest(OpenAI::Model::GPT_4_1_Mini, "Summarize this
 ```
 
 **Available models:**
+- GPT_5, GPT_5_Mini, GPT_5_Nano
 - O3, O3_Mini
 - O1, O1_Mini, O1_Preview, O1_Pro
 - O4_Mini, O4_Mini_Deep_Research
@@ -307,6 +308,9 @@ The library provides type-safe model selection using the `OpenAI::Model` enum:
 
 ```cpp
 // Available model enums
+OpenAI::Model::GPT_5          // gpt-5 - Next-generation model (reasoning)
+OpenAI::Model::GPT_5_Mini     // gpt-5-mini - Cost-effective GPT-5
+OpenAI::Model::GPT_5_Nano     // gpt-5-nano - Fastest GPT-5
 OpenAI::Model::GPT_4_1        // gpt-4.1 - Latest model with superior coding and structured outputs
 OpenAI::Model::GPT_4_1_Mini   // gpt-4.1-mini - Balanced performance and cost
 OpenAI::Model::GPT_4_1_Nano   // gpt-4.1-nano - Fastest and cheapest option

include/openai/OpenAITypes.h

@@ -18,7 +18,9 @@ namespace OpenAI {
  */
 enum class Model {
     // GPT-5 series (Latest - 2025)
-    GPT_5,  // gpt-5 - Next-generation model
+    GPT_5,       // gpt-5 - Next-generation model
+    GPT_5_Mini,  // gpt-5-mini - Smaller, cost-effective variant
+    GPT_5_Nano,  // gpt-5-nano - Fastest and cheapest GPT-5 variant
 
     // O3 series (Latest - 2025)
     O3,       // o3 - Latest reasoning model
@@ -61,6 +63,10 @@ inline std::string toString(Model model) {
     switch (model) {
         case Model::GPT_5:
             return "gpt-5";
+        case Model::GPT_5_Mini:
+            return "gpt-5-mini";
+        case Model::GPT_5_Nano:
+            return "gpt-5-nano";
         case Model::O3:
             return "o3";
         case Model::O3_Mini:
@@ -102,6 +108,8 @@ inline std::string toString(Model model) {
  */
 inline Model modelFromString(const std::string& modelStr) {
     if (modelStr == "gpt-5") return Model::GPT_5;
+    if (modelStr == "gpt-5-mini") return Model::GPT_5_Mini;
+    if (modelStr == "gpt-5-nano") return Model::GPT_5_Nano;
     if (modelStr == "o3") return Model::O3;
     if (modelStr == "o3-mini") return Model::O3_Mini;
     if (modelStr == "o1") return Model::O1;
@@ -126,6 +134,8 @@ inline Model modelFromString(const std::string& modelStr) {
 inline bool supportsStructuredOutputs(Model model) {
     switch (model) {
         case Model::GPT_5:
+        case Model::GPT_5_Mini:
+        case Model::GPT_5_Nano:
         case Model::O3:
         case Model::O3_Mini:
         case Model::O1: